[PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page

[PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page

[Zhong, Xin]

This problem is found in meego testing:
http://bugs.meego.com/show_bug.cgi?id=6672
A file in btrfs is mmaped and the mmaped buffer is passed to pwrite to write to the same page
of the same file. In btrfs_file_aio_write(), the pages is locked by prepare_pages(). So when
btrfs_copy_from_user() is called, page fault happens and the same page needs to be locked again
in filemap_fault(). The fix is to move iov_iter_fault_in_readable() before prepage_pages() to make page
fault happen before pages are locked. And also disable page fault in critical region in
btrfs_copy_from_user().

Reviewed-by: Yan, Zheng<zheng.z.yan@intel.com>
Signed-off-by: Zhong, Xin <xin.zhong@intel.com>
---
 fs/btrfs/file.c |   92 ++++++++++++++++++++++++++++++++++++-------------------
 1 files changed, 60 insertions(+), 32 deletions(-)

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index c1faded..66836d8 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -48,30 +48,34 @@ static noinline int btrfs_copy_from_user(loff_t pos, int num_pages,
 					 struct page **prepared_pages,
 					 struct iov_iter *i)
 {
-	size_t copied;
+	size_t copied = 0;
 	int pg = 0;
 	int offset = pos & (PAGE_CACHE_SIZE - 1);
+	int total_copied = 0;
 
 	while (write_bytes > 0) {
 		size_t count = min_t(size_t,
 				     PAGE_CACHE_SIZE - offset, write_bytes);
 		struct page *page = prepared_pages[pg];
-again:
-		if (unlikely(iov_iter_fault_in_readable(i, count)))
-			return -EFAULT;
-
-		/* Copy data from userspace to the current page */
-		copied = iov_iter_copy_from_user(page, i, offset, count);
+		/*
+		 * Copy data from userspace to the current page
+		 *
+		 * Disable pagefault to avoid recursive lock since
+		 * the pages are already locked
+		 */
+		pagefault_disable();
+		copied = iov_iter_copy_from_user_atomic(page, i, offset, count);
+		pagefault_enable();
 
 		/* Flush processor's dcache for this page */
 		flush_dcache_page(page);
 		iov_iter_advance(i, copied);
 		write_bytes -= copied;
+		total_copied += copied;
 
+		/* Return to btrfs_file_aio_write to fault page */
 		if (unlikely(copied == 0)) {
-			count = min_t(size_t, PAGE_CACHE_SIZE - offset,
-				      iov_iter_single_seg_count(i));
-			goto again;
+			break;
 		}
 
 		if (unlikely(copied < PAGE_CACHE_SIZE - offset)) {
@@ -81,7 +85,7 @@ again:
 			offset = 0;
 		}
 	}
-	return 0;
+	return total_copied;
 }
 
 /*
@@ -854,6 +858,8 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
 	unsigned long last_index;
 	int will_write;
 	int buffered = 0;
+	int copied = 0;
+	int dirty_pages = 0;
 
 	will_write = ((file->f_flags & O_DSYNC) || IS_SYNC(inode) ||
 		      (file->f_flags & O_DIRECT));
@@ -970,7 +976,17 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
 		WARN_ON(num_pages > nrptrs);
 		memset(pages, 0, sizeof(struct page *) * nrptrs);
 
-		ret = btrfs_delalloc_reserve_space(inode, write_bytes);
+		/*
+		 * Fault pages before locking them in prepare_pages
+		 * to avoid recursive lock
+		 */
+		if (unlikely(iov_iter_fault_in_readable(&i, write_bytes))) {
+			ret = -EFAULT;
+			goto out;
+		}
+
+		ret = btrfs_delalloc_reserve_space(inode,
+					num_pages << PAGE_CACHE_SHIFT);
 		if (ret)
 			goto out;
 
@@ -978,37 +994,49 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
 				    pos, first_index, last_index,
 				    write_bytes);
 		if (ret) {
-			btrfs_delalloc_release_space(inode, write_bytes);
+			btrfs_delalloc_release_space(inode,
+					num_pages << PAGE_CACHE_SHIFT);
 			goto out;
 		}
 
-		ret = btrfs_copy_from_user(pos, num_pages,
+		copied = btrfs_copy_from_user(pos, num_pages,
 					   write_bytes, pages, &i);
-		if (ret == 0) {
+		dirty_pages = (copied + PAGE_CACHE_SIZE - 1) >>
+					PAGE_CACHE_SHIFT;
+
+		if (num_pages > dirty_pages) {
+			if (copied > 0)
+				atomic_inc(
+					&BTRFS_I(inode)->outstanding_extents);
+			btrfs_delalloc_release_space(inode,
+					(num_pages - dirty_pages) <<
+					PAGE_CACHE_SHIFT);
+		}
+
+		if (copied > 0) {
 			dirty_and_release_pages(NULL, root, file, pages,
-						num_pages, pos, write_bytes);
+						dirty_pages, pos, copied);
 		}
 
 		btrfs_drop_pages(pages, num_pages);
-		if (ret) {
-			btrfs_delalloc_release_space(inode, write_bytes);
-			goto out;
-		}
 
-		if (will_write) {
-			filemap_fdatawrite_range(inode->i_mapping, pos,
-						 pos + write_bytes - 1);
-		} else {
-			balance_dirty_pages_ratelimited_nr(inode->i_mapping,
-							   num_pages);
-			if (num_pages <
-			    (root->leafsize >> PAGE_CACHE_SHIFT) + 1)
-				btrfs_btree_balance_dirty(root, 1);
-			btrfs_throttle(root);
+		if (copied > 0) {
+			if (will_write) {
+				filemap_fdatawrite_range(inode->i_mapping, pos,
+							 pos + copied - 1);
+			} else {
+				balance_dirty_pages_ratelimited_nr(
+							inode->i_mapping,
+							dirty_pages);
+				if (dirty_pages <
+				(root->leafsize >> PAGE_CACHE_SHIFT) + 1)
+					btrfs_btree_balance_dirty(root, 1);
+				btrfs_throttle(root);
+			}
 		}
 
-		pos += write_bytes;
-		num_written += write_bytes;
+		pos += copied;
+		num_written += copied;
 
 		cond_resched();
 	}
-- 
1.6.2.2

Re: [PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page

[Johannes Hirte]

On Thursday 09 December 2010 10:30:14 Zhong, Xin wrote:
> This problem is found in meego testing:
> http://bugs.meego.com/show_bug.cgi?id=6672
> A file in btrfs is mmaped and the mmaped buffer is passed to pwrite to
> write to the same page of the same file. In btrfs_file_aio_write(), the
> pages is locked by prepare_pages(). So when btrfs_copy_from_user() is
> called, page fault happens and the same page needs to be locked again in
> filemap_fault(). The fix is to move iov_iter_fault_in_readable() before
> prepage_pages() to make page fault happen before pages are locked. And
> also disable page fault in critical region in btrfs_copy_from_user().
> 
> Reviewed-by: Yan, Zheng<zheng.z.yan@intel.com>
> Signed-off-by: Zhong, Xin <xin.zhong@intel.com>
> ---
>  fs/btrfs/file.c |   92
> ++++++++++++++++++++++++++++++++++++------------------- 1 files changed,
> 60 insertions(+), 32 deletions(-)
> 
> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> index c1faded..66836d8 100644
> --- a/fs/btrfs/file.c
> +++ b/fs/btrfs/file.c
> @@ -48,30 +48,34 @@ static noinline int btrfs_copy_from_user(loff_t pos,
> int num_pages, struct page **prepared_pages,
>  					 struct iov_iter *i)
>  {
> -	size_t copied;
> +	size_t copied = 0;
>  	int pg = 0;
>  	int offset = pos & (PAGE_CACHE_SIZE - 1);
> +	int total_copied = 0;
> 
>  	while (write_bytes > 0) {
>  		size_t count = min_t(size_t,
>  				     PAGE_CACHE_SIZE - offset, write_bytes);
>  		struct page *page = prepared_pages[pg];
> -again:
> -		if (unlikely(iov_iter_fault_in_readable(i, count)))
> -			return -EFAULT;
> -
> -		/* Copy data from userspace to the current page */
> -		copied = iov_iter_copy_from_user(page, i, offset, count);
> +		/*
> +		 * Copy data from userspace to the current page
> +		 *
> +		 * Disable pagefault to avoid recursive lock since
> +		 * the pages are already locked
> +		 */
> +		pagefault_disable();
> +		copied = iov_iter_copy_from_user_atomic(page, i, offset, count);
> +		pagefault_enable();
> 
>  		/* Flush processor's dcache for this page */
>  		flush_dcache_page(page);
>  		iov_iter_advance(i, copied);
>  		write_bytes -= copied;
> +		total_copied += copied;
> 
> +		/* Return to btrfs_file_aio_write to fault page */
>  		if (unlikely(copied == 0)) {
> -			count = min_t(size_t, PAGE_CACHE_SIZE - offset,
> -				      iov_iter_single_seg_count(i));
> -			goto again;
> +			break;
>  		}
> 
>  		if (unlikely(copied < PAGE_CACHE_SIZE - offset)) {
> @@ -81,7 +85,7 @@ again:
>  			offset = 0;
>  		}
>  	}
> -	return 0;
> +	return total_copied;
>  }
> 
>  /*
> @@ -854,6 +858,8 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
>  	unsigned long last_index;
>  	int will_write;
>  	int buffered = 0;
> +	int copied = 0;
> +	int dirty_pages = 0;
> 
>  	will_write = ((file->f_flags & O_DSYNC) || IS_SYNC(inode) ||
>  		      (file->f_flags & O_DIRECT));
> @@ -970,7 +976,17 @@ static ssize_t btrfs_file_aio_write(struct kiocb
> *iocb, WARN_ON(num_pages > nrptrs);
>  		memset(pages, 0, sizeof(struct page *) * nrptrs);
> 
> -		ret = btrfs_delalloc_reserve_space(inode, write_bytes);
> +		/*
> +		 * Fault pages before locking them in prepare_pages
> +		 * to avoid recursive lock
> +		 */
> +		if (unlikely(iov_iter_fault_in_readable(&i, write_bytes))) {
> +			ret = -EFAULT;
> +			goto out;
> +		}
> +
> +		ret = btrfs_delalloc_reserve_space(inode,
> +					num_pages << PAGE_CACHE_SHIFT);
>  		if (ret)
>  			goto out;
> 
> @@ -978,37 +994,49 @@ static ssize_t btrfs_file_aio_write(struct kiocb
> *iocb, pos, first_index, last_index,
>  				    write_bytes);
>  		if (ret) {
> -			btrfs_delalloc_release_space(inode, write_bytes);
> +			btrfs_delalloc_release_space(inode,
> +					num_pages << PAGE_CACHE_SHIFT);
>  			goto out;
>  		}
> 
> -		ret = btrfs_copy_from_user(pos, num_pages,
> +		copied = btrfs_copy_from_user(pos, num_pages,
>  					   write_bytes, pages, &i);
> -		if (ret == 0) {
> +		dirty_pages = (copied + PAGE_CACHE_SIZE - 1) >>
> +					PAGE_CACHE_SHIFT;
> +
> +		if (num_pages > dirty_pages) {
> +			if (copied > 0)
> +				atomic_inc(
> +					&BTRFS_I(inode)->outstanding_extents);
> +			btrfs_delalloc_release_space(inode,
> +					(num_pages - dirty_pages) <<
> +					PAGE_CACHE_SHIFT);
> +		}
> +
> +		if (copied > 0) {
>  			dirty_and_release_pages(NULL, root, file, pages,
> -						num_pages, pos, write_bytes);
> +						dirty_pages, pos, copied);
>  		}
> 
>  		btrfs_drop_pages(pages, num_pages);
> -		if (ret) {
> -			btrfs_delalloc_release_space(inode, write_bytes);
> -			goto out;
> -		}
> 
> -		if (will_write) {
> -			filemap_fdatawrite_range(inode->i_mapping, pos,
> -						 pos + write_bytes - 1);
> -		} else {
> -			balance_dirty_pages_ratelimited_nr(inode->i_mapping,
> -							   num_pages);
> -			if (num_pages <
> -			    (root->leafsize >> PAGE_CACHE_SHIFT) + 1)
> -				btrfs_btree_balance_dirty(root, 1);
> -			btrfs_throttle(root);
> +		if (copied > 0) {
> +			if (will_write) {
> +				filemap_fdatawrite_range(inode->i_mapping, pos,
> +							 pos + copied - 1);
> +			} else {
> +				balance_dirty_pages_ratelimited_nr(
> +							inode->i_mapping,
> +							dirty_pages);
> +				if (dirty_pages <
> +				(root->leafsize >> PAGE_CACHE_SHIFT) + 1)
> +					btrfs_btree_balance_dirty(root, 1);
> +				btrfs_throttle(root);
> +			}
>  		}
> 
> -		pos += write_bytes;
> -		num_written += write_bytes;
> +		pos += copied;
> +		num_written += copied;
> 
>  		cond_resched();
>  	}

This patch breaks one of my Gentoo boxes. When I try to install/update via 
emerge, some packages hang. It seems that it's always a "svn info" process 
that is stuck in kernel eating 100% CPU. I don't know how svn is involved 
here, but reverting this patch makes the system work again. I'll try to get a 
simple testcase.

regards,
  Johannes

Re: [PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page

[Maria Wikström]

tor 2011-01-27 klockan 14:09 +0100 skrev Johannes Hirte: 
> On Thursday 09 December 2010 10:30:14 Zhong, Xin wrote:
> > This problem is found in meego testing:
> > http://bugs.meego.com/show_bug.cgi?id=6672
> > A file in btrfs is mmaped and the mmaped buffer is passed to pwrite to
> > write to the same page of the same file. In btrfs_file_aio_write(), the
> > pages is locked by prepare_pages(). So when btrfs_copy_from_user() is
> > called, page fault happens and the same page needs to be locked again in
> > filemap_fault(). The fix is to move iov_iter_fault_in_readable() before
> > prepage_pages() to make page fault happen before pages are locked. And
> > also disable page fault in critical region in btrfs_copy_from_user().
> > 
> > Reviewed-by: Yan, Zheng<zheng.z.yan@intel.com>
> > Signed-off-by: Zhong, Xin <xin.zhong@intel.com>
> > ---
> >  fs/btrfs/file.c |   92
> > ++++++++++++++++++++++++++++++++++++------------------- 1 files changed,
> > 60 insertions(+), 32 deletions(-)
> > 
> > diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> > index c1faded..66836d8 100644
> > --- a/fs/btrfs/file.c
> > +++ b/fs/btrfs/file.c
> > @@ -48,30 +48,34 @@ static noinline int btrfs_copy_from_user(loff_t pos,
> > int num_pages, struct page **prepared_pages,
> >  					 struct iov_iter *i)
> >  {
> > -	size_t copied;
> > +	size_t copied = 0;
> >  	int pg = 0;
> >  	int offset = pos & (PAGE_CACHE_SIZE - 1);
> > +	int total_copied = 0;
> > 
> >  	while (write_bytes > 0) {
> >  		size_t count = min_t(size_t,
> >  				     PAGE_CACHE_SIZE - offset, write_bytes);
> >  		struct page *page = prepared_pages[pg];
> > -again:
> > -		if (unlikely(iov_iter_fault_in_readable(i, count)))
> > -			return -EFAULT;
> > -
> > -		/* Copy data from userspace to the current page */
> > -		copied = iov_iter_copy_from_user(page, i, offset, count);
> > +		/*
> > +		 * Copy data from userspace to the current page
> > +		 *
> > +		 * Disable pagefault to avoid recursive lock since
> > +		 * the pages are already locked
> > +		 */
> > +		pagefault_disable();
> > +		copied = iov_iter_copy_from_user_atomic(page, i, offset, count);
> > +		pagefault_enable();
> > 
> >  		/* Flush processor's dcache for this page */
> >  		flush_dcache_page(page);
> >  		iov_iter_advance(i, copied);
> >  		write_bytes -= copied;
> > +		total_copied += copied;
> > 
> > +		/* Return to btrfs_file_aio_write to fault page */
> >  		if (unlikely(copied == 0)) {
> > -			count = min_t(size_t, PAGE_CACHE_SIZE - offset,
> > -				      iov_iter_single_seg_count(i));
> > -			goto again;
> > +			break;
> >  		}
> > 
> >  		if (unlikely(copied < PAGE_CACHE_SIZE - offset)) {
> > @@ -81,7 +85,7 @@ again:
> >  			offset = 0;
> >  		}
> >  	}
> > -	return 0;
> > +	return total_copied;
> >  }
> > 
> >  /*
> > @@ -854,6 +858,8 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
> >  	unsigned long last_index;
> >  	int will_write;
> >  	int buffered = 0;
> > +	int copied = 0;
> > +	int dirty_pages = 0;
> > 
> >  	will_write = ((file->f_flags & O_DSYNC) || IS_SYNC(inode) ||
> >  		      (file->f_flags & O_DIRECT));
> > @@ -970,7 +976,17 @@ static ssize_t btrfs_file_aio_write(struct kiocb
> > *iocb, WARN_ON(num_pages > nrptrs);
> >  		memset(pages, 0, sizeof(struct page *) * nrptrs);
> > 
> > -		ret = btrfs_delalloc_reserve_space(inode, write_bytes);
> > +		/*
> > +		 * Fault pages before locking them in prepare_pages
> > +		 * to avoid recursive lock
> > +		 */
> > +		if (unlikely(iov_iter_fault_in_readable(&i, write_bytes))) {
> > +			ret = -EFAULT;
> > +			goto out;
> > +		}
> > +
> > +		ret = btrfs_delalloc_reserve_space(inode,
> > +					num_pages << PAGE_CACHE_SHIFT);
> >  		if (ret)
> >  			goto out;
> > 
> > @@ -978,37 +994,49 @@ static ssize_t btrfs_file_aio_write(struct kiocb
> > *iocb, pos, first_index, last_index,
> >  				    write_bytes);
> >  		if (ret) {
> > -			btrfs_delalloc_release_space(inode, write_bytes);
> > +			btrfs_delalloc_release_space(inode,
> > +					num_pages << PAGE_CACHE_SHIFT);
> >  			goto out;
> >  		}
> > 
> > -		ret = btrfs_copy_from_user(pos, num_pages,
> > +		copied = btrfs_copy_from_user(pos, num_pages,
> >  					   write_bytes, pages, &i);
> > -		if (ret == 0) {
> > +		dirty_pages = (copied + PAGE_CACHE_SIZE - 1) >>
> > +					PAGE_CACHE_SHIFT;
> > +
> > +		if (num_pages > dirty_pages) {
> > +			if (copied > 0)
> > +				atomic_inc(
> > +					&BTRFS_I(inode)->outstanding_extents);
> > +			btrfs_delalloc_release_space(inode,
> > +					(num_pages - dirty_pages) <<
> > +					PAGE_CACHE_SHIFT);
> > +		}
> > +
> > +		if (copied > 0) {
> >  			dirty_and_release_pages(NULL, root, file, pages,
> > -						num_pages, pos, write_bytes);
> > +						dirty_pages, pos, copied);
> >  		}
> > 
> >  		btrfs_drop_pages(pages, num_pages);
> > -		if (ret) {
> > -			btrfs_delalloc_release_space(inode, write_bytes);
> > -			goto out;
> > -		}
> > 
> > -		if (will_write) {
> > -			filemap_fdatawrite_range(inode->i_mapping, pos,
> > -						 pos + write_bytes - 1);
> > -		} else {
> > -			balance_dirty_pages_ratelimited_nr(inode->i_mapping,
> > -							   num_pages);
> > -			if (num_pages <
> > -			    (root->leafsize >> PAGE_CACHE_SHIFT) + 1)
> > -				btrfs_btree_balance_dirty(root, 1);
> > -			btrfs_throttle(root);
> > +		if (copied > 0) {
> > +			if (will_write) {
> > +				filemap_fdatawrite_range(inode->i_mapping, pos,
> > +							 pos + copied - 1);
> > +			} else {
> > +				balance_dirty_pages_ratelimited_nr(
> > +							inode->i_mapping,
> > +							dirty_pages);
> > +				if (dirty_pages <
> > +				(root->leafsize >> PAGE_CACHE_SHIFT) + 1)
> > +					btrfs_btree_balance_dirty(root, 1);
> > +				btrfs_throttle(root);
> > +			}
> >  		}
> > 
> > -		pos += write_bytes;
> > -		num_written += write_bytes;
> > +		pos += copied;
> > +		num_written += copied;
> > 
> >  		cond_resched();
> >  	}
> 
> This patch breaks one of my Gentoo boxes. When I try to install/update via 
> emerge, some packages hang. It seems that it's always a "svn info" process 
> that is stuck in kernel eating 100% CPU. I don't know how svn is involved 
> here, but reverting this patch makes the system work again. I'll try to get a 
> simple testcase.
> 
> regards,
>   Johannes

The same thing happens here. The only way to kill the process (svn info)
is to restart the computer. Running vanilla 2.6.37 without patches.

#strace emerge libgcrypt
-- cut -- 
open("/var/tmp/portage/dev-libs/libgcrypt-1.4.6/temp/build.log",
O_WRONLY|O_CREAT|O_APPEND|O_LARGEFILE, 0666) = 7
fstat64(7, {st_mode=S_IFREG|0660, st_size=416, ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1,
0) = 0xb713a000
fstat64(7, {st_mode=S_IFREG|0660, st_size=416, ...}) = 0
_llseek(7, 416, [416], SEEK_SET)        = 0
fstat64(7, {st_mode=S_IFREG|0660, st_size=416, ...}) = 0
stat64("/var/tmp/portage/dev-libs/libgcrypt-1.4.6/temp/build.log",
{st_mode=S_IFREG|0660, st_size=416, ...}) = 0
dup(1)                                  = 8
fcntl64(8, F_GETFL)                     = 0x2 (flags O_RDWR)
fstat64(8, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 3), ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1,
0) = 0xb7005000
_llseek(8, 0, 0xbff80cfc, SEEK_CUR)     = -1 ESPIPE (Illegal seek)
fstat64(8, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 3), ...}) = 0
stat64("/var/tmp/portage/dev-libs/libgcrypt-1.4.6/temp/environment",
{st_mode=S_IFREG|0664, st_size=105970, ...}) = 0
clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|
SIGCHLD, child_tidptr=0xb7430728) = 11665
close(6)                                = 0
gettimeofday({1296162836, 126192}, NULL) = 0
poll([{fd=3, events=POLLIN|POLLERR|POLLHUP|POLLNVAL}, {fd=5,
events=POLLIN|POLLERR|POLLHUP|POLLNVAL}], 2, 3000) = 1 ([{fd=5,
revents=POLLIN}])
read(5, ">>> Preparing source in /var/tmp"..., 4096) = 91
read(5, 0xb713b000, 4096)               = -1 EAGAIN (Resource
temporarily unavailable)
write(8, ">>> Preparing source in /var/tmp"..., 91>>> Preparing source
in /var/tmp/portage/dev-libs/libgcrypt-1.4.6/work/libgcrypt-1.4.6 ...
) = 91
write(7, ">>> Preparing source in /var/tmp"..., 91) = 91
poll([{fd=3, events=POLLIN|POLLERR|POLLHUP|POLLNVAL}, {fd=5,
events=POLLIN|POLLERR|POLLHUP|POLLNVAL}], 2, 3000) = 0 (Timeout)
poll([{fd=3, events=POLLIN|POLLERR|POLLHUP|POLLNVAL}, {fd=5,
events=POLLIN|POLLERR|POLLHUP|POLLNVAL}], 2, 3000) = 0 (Timeout)
poll([{fd=3, events=POLLIN|POLLERR|POLLHUP|POLLNVAL}, {fd=5,
events=POLLIN|POLLERR|POLLHUP|POLLNVAL}], 2, 3000) = 0 (Timeout)

The last line is repeated every 3sec.

// Maria

RE: [PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page

[Zhong, Xin]

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Re: [PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page

[Johannes Hirte]

On Friday 28 January 2011 02:26:43 Zhong, Xin wrote:
> Please try the fix in below link:
> http://www.spinics.net/lists/linux-btrfs/msg08051.html
> 
> Thanks!

This doesn't fix it for me. At least there is a difference. Whereas the svn 
process started consuming 100% CPU without any further interaction before, the 
system just hang now. The svn process starts eating the CPU when I cancel the 
emerge via ctrl-c. Additional I see a flush-btrfs task now consuming CPU time.

regards,
  Johannes

RE: [PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page

[Zhong, Xin]
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LWJ0cmZzIHRhc2sgbm93IGNvbnN1bWluZyBDUFUgdGltZS4NCg0KcmVnYXJkcywNCiAgSm9oYW5u
ZXMNCg==

Re: [PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page

[Maria Wikström]

fre 2011-01-28 klockan 03:54 +0100 skrev Johannes Hirte: 
> On Friday 28 January 2011 02:26:43 Zhong, Xin wrote:
> > Please try the fix in below link:
> > http://www.spinics.net/lists/linux-btrfs/msg08051.html
> > 
> > Thanks!
> 
> This doesn't fix it for me. At least there is a difference. Whereas the svn 
> process started consuming 100% CPU without any further interaction before, the 
> system just hang now. The svn process starts eating the CPU when I cancel the 
> emerge via ctrl-c. Additional I see a flush-btrfs task now consuming CPU time.
> 
> regards,
>   Johannes
> --
> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 

The patch makes the process exit cleanly but complains that there is no
space left. It should be a few GB but it is only a few MB!? I delete 5GB
and controls that the space is usable. Try again but this time it almost
hangs the system, I can blink the leds and move the mouse but noting
more. 
I boot 2.6.36.1 and use a snapshot as root, "emerge libgcrypt" compiles
and installs fine. Boots back into 2.6.37 and try again and the system
hangs again.

// Maria

Re: [PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page

[Rui Miguel Silva]

On Friday, January 28, 2011 04:47:21 pm Maria Wikstr=C3=B6m wrote:
> fre 2011-01-28 klockan 03:54 +0100 skrev Johannes Hirte:
> > On Friday 28 January 2011 02:26:43 Zhong, Xin wrote:
> > > Please try the fix in below link:
> > > http://www.spinics.net/lists/linux-btrfs/msg08051.html
> > >=20
> > > Thanks!
> >=20
> > This doesn't fix it for me. At least there is a difference. Whereas=
 the
> > svn process started consuming 100% CPU without any further interact=
ion
> > before, the system just hang now. The svn process starts eating the=
 CPU
> > when I cancel the emerge via ctrl-c. Additional I see a flush-btrfs=
 task
> > now consuming CPU time.
> >=20
> > regards,
> >=20
> >   Johannes
> >=20
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-btr=
fs" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
>=20
> The patch makes the process exit cleanly but complains that there is =
no
> space left. It should be a few GB but it is only a few MB!? I delete =
5GB
> and controls that the space is usable. Try again but this time it alm=
ost
> hangs the system, I can blink the leds and move the mouse but noting
> more.
> I boot 2.6.36.1 and use a snapshot as root, "emerge libgcrypt" compil=
es
> and installs fine. Boots back into 2.6.37 and try again and the syste=
m
> hangs again.
>=20
> // Maria
>=20

Hi Maria,
I had something similar with vanilla 2.6.37 just for running:
cscope -R -b -q

allways hang complety the process, only solution reboot.
I just applied the  btrfs patches that arrived in the main tree between=
 the=20
2.6.37 and 2.6.38-rc1 and they seem to fix the issue.

I did not have the time to try to found which patch fixed the problem.

Hope this could help you.

Cheers,
  //Rui
--
To unsubscribe from this list: send the line "unsubscribe linux-btrfs" =
in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: [PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page

[Maria Wikström]

fre 2011-01-28 klockan 18:27 +0000 skrev Rui Miguel Silva:=20
> On Friday, January 28, 2011 04:47:21 pm Maria Wikstr=C3=B6m wrote:
> > fre 2011-01-28 klockan 03:54 +0100 skrev Johannes Hirte:
> > > On Friday 28 January 2011 02:26:43 Zhong, Xin wrote:
> > > > Please try the fix in below link:
> > > > http://www.spinics.net/lists/linux-btrfs/msg08051.html
> > > >=20
> > > > Thanks!
> > >=20
> > > This doesn't fix it for me. At least there is a difference. Where=
as the
> > > svn process started consuming 100% CPU without any further intera=
ction
> > > before, the system just hang now. The svn process starts eating t=
he CPU
> > > when I cancel the emerge via ctrl-c. Additional I see a flush-btr=
fs task
> > > now consuming CPU time.
> > >=20
> > > regards,
> > >=20
> > >   Johannes
> > >=20
> > > --
> > > To unsubscribe from this list: send the line "unsubscribe linux-b=
trfs" in
> > > the body of a message to majordomo@vger.kernel.org
> > > More majordomo info at  http://vger.kernel.org/majordomo-info.htm=
l
> >=20
> > The patch makes the process exit cleanly but complains that there i=
s no
> > space left. It should be a few GB but it is only a few MB!? I delet=
e 5GB
> > and controls that the space is usable. Try again but this time it a=
lmost
> > hangs the system, I can blink the leds and move the mouse but notin=
g
> > more.
> > I boot 2.6.36.1 and use a snapshot as root, "emerge libgcrypt" comp=
iles
> > and installs fine. Boots back into 2.6.37 and try again and the sys=
tem
> > hangs again.
> >=20
> > // Maria
> >=20
>=20
> Hi Maria,
> I had something similar with vanilla 2.6.37 just for running:
> cscope -R -b -q
>=20
> allways hang complety the process, only solution reboot.
> I just applied the  btrfs patches that arrived in the main tree betwe=
en the=20
> 2.6.37 and 2.6.38-rc1 and they seem to fix the issue.
>=20
> I did not have the time to try to found which patch fixed the problem=
=2E
>=20
> Hope this could help you.
>=20
> Cheers,
>   //Rui

I have tried with both vanilla 2.6.38-rc2 and btrfs-unstable from git,
both having the problem.=20

Btrfs-unstable with the patch above behaves differently. The process ca=
n
be killed with Ctrl + C but then the terminal and gnome-pty-helper eats
cpu instead. They can be killed with SysRq + i together with everything
else.

// Maria


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To unsubscribe from this list: send the line "unsubscribe linux-btrfs" =
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Re: [PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page

[Johannes Hirte]

On Friday 28 January 2011 04:53:24 Zhong, Xin wrote:
> Could you describe the steps to recreate it?
> It will be a great help for me to look further. Thanks!

It's a little strange. I have to systems with btrfs, both Gentoo-based. One is 
affected by this bug the other is not. On the affected system it is enough to do 
a 'emerge dev-libs/libgcrypt' that should normaly compile and install 
libgcrypt. The emerge command is part of portage, the package management of 
Gentoo. 
The strace output looks similar to the one from Maria:

open("/home/tmp/portage/dev-libs/libgcrypt-1.4.6/.ipc_in", O_RDONLY|
O_NONBLOCK|O_LARGEFILE) = 3
fstat64(3, {st_mode=S_IFIFO|0770, st_size=0, ...}) = 0
ioctl(3, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, 
0xbff5f678) = -1 EINVAL (Invalid argument)
open("/dev/ptmx", O_RDWR)               = 5
ioctl(5, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, 
{B38400 opost isig icanon echo ...}) = 0
ioctl(5, TIOCGPTN, [2])                 = 0
stat64("/dev/pts/2", {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 2), ...}) = 0
getuid32()                              = 0
ioctl(5, TIOCSPTLCK, [0])               = 0
ioctl(5, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, 
{B38400 opost isig icanon echo ...}) = 0
ioctl(5, TIOCGPTN, [2])                 = 0
stat64("/dev/pts/2", {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 2), ...}) = 0
open("/dev/pts/2", O_RDWR|O_NOCTTY)     = 6
ioctl(6, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, 
{B38400 opost isig icanon echo ...}) = 0
ioctl(6, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, 
{B38400 opost isig icanon echo ...}) = 0
ioctl(6, SNDCTL_TMR_START or SNDRV_TIMER_IOCTL_TREAD or TCSETS, {B38400 -opost 
isig icanon echo ...}) = 0
ioctl(1, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, 
{B38400 opost isig icanon echo ...}) = 0
ioctl(1, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, 
{B38400 opost isig icanon echo ...}) = 0
ioctl(1, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, 
{B38400 opost isig icanon echo ...}) = 0
stat64("/root/.terminfo", 0xbff5e790)   = -1 ENOENT (No such file or directory)
stat64("/etc/terminfo", {st_mode=S_IFDIR|0755, st_size=14, ...}) = 0
access("/etc/terminfo/x/xterm", R_OK)   = 0
open("/etc/terminfo/x/xterm", O_RDONLY|O_LARGEFILE) = 7
read(7, "\32\0010\0&\0\17\0\235\1l\5xterm|xterm terminal"..., 4097) = 3258
close(7)                                = 0
ioctl(1, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, 
{B38400 opost isig icanon echo ...}) = 0
ioctl(1, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, 
{B38400 opost isig icanon echo ...}) = 0
ioctl(1, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, 
{B38400 opost isig icanon echo ...}) = 0
ioctl(1, TIOCGWINSZ, {ws_row=40, ws_col=207, ws_xpixel=0, ws_ypixel=0}) = 0
access("/usr/local/sbin/stty", X_OK)    = -1 ENOENT (No such file or directory)
access("/usr/local/bin/stty", X_OK)     = -1 ENOENT (No such file or directory)
access("/usr/sbin/stty", X_OK)          = -1 ENOENT (No such file or directory)
access("/usr/bin/stty", X_OK)           = -1 ENOENT (No such file or directory)
access("/sbin/stty", X_OK)              = -1 ENOENT (No such file or directory)
access("/bin/stty", X_OK)               = 0
stat64("/bin/stty", {st_mode=S_IFREG|0755, st_size=58836, ...}) = 0
clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, 
child_tidptr=0xb753d728) = 2752
waitpid(2752, [{WIFEXITED(s) && WEXITSTATUS(s) == 0}], 0) = 2752
--- SIGCHLD (Child exited) @ 0 (0) ---
fcntl64(5, F_GETFL)                     = 0x2 (flags O_RDWR)
fcntl64(5, F_SETFL, O_RDWR|O_NONBLOCK)  = 0
fstat64(5, {st_mode=S_IFCHR|0666, st_rdev=makedev(5, 2), ...}) = 0
ioctl(5, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, 
{B38400 -opost isig icanon echo ...}) = 0
open("/home/tmp/portage/dev-libs/libgcrypt-1.4.6/temp/build.log", O_WRONLY|
O_CREAT|O_APPEND|O_LARGEFILE, 0666) = 7
fstat64(7, {st_mode=S_IFREG|0660, st_size=480, ...}) = 0
_llseek(7, 0, [480], SEEK_END)          = 0
ioctl(7, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, 
0xbff5fad8) = -1 ENOTTY (Inappropriate ioctl for device)
fstat64(7, {st_mode=S_IFREG|0660, st_size=480, ...}) = 0
_llseek(7, 0, [480], SEEK_CUR)          = 0
stat64("/home/tmp/portage/dev-libs/libgcrypt-1.4.6/temp/build.log", 
{st_mode=S_IFREG|0660, st_size=480, ...}) = 0
dup(1)                                  = 8
fstat64(8, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 0), ...}) = 0
ioctl(8, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or TCGETS, 
{B38400 opost isig icanon echo ...}) = 0
fstat64(8, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 0), ...}) = 0
_llseek(8, 0, 0xbff5f820, SEEK_CUR)     = -1 ESPIPE (Illegal seek)
stat64("/home/tmp/portage/dev-libs/libgcrypt-1.4.6/temp/environment", 
{st_mode=S_IFREG|0664, st_size=106597, ...}) = 0
clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, 
child_tidptr=0xb753d728) = 2753
close(6)                                = 0
gettimeofday({1296577457, 11117}, NULL) = 0
poll([{fd=3, events=POLLIN|POLLERR|POLLHUP|POLLNVAL}, {fd=5, events=POLLIN|
POLLERR|POLLHUP|POLLNVAL}], 2, 3000) = 1 ([{fd=5, revents=POLLIN}])
read(5, ">>> Preparing source in /home/tm"..., 4096) = 92
write(8, ">>> Preparing source in /home/tm"..., 92) = 92
write(7, ">>> Preparing source in /home/tm"..., 92) = 92
poll([{fd=3, events=POLLIN|POLLERR|POLLHUP|POLLNVAL}, {fd=5, events=POLLIN|
POLLERR|POLLHUP|POLLNVAL}], 2, 3000) = 0 (Timeout)
poll([{fd=3, events=POLLIN|POLLERR|POLLHUP|POLLNVAL}, {fd=5, events=POLLIN|
POLLERR|POLLHUP|POLLNVAL}], 2, 3000) = 0 (Timeout)
poll([{fd=3, events=POLLIN|POLLERR|POLLHUP|POLLNVAL}, {fd=5, events=POLLIN|
POLLERR|POLLHUP|POLLNVAL}], 2, 3000) = 0 (Timeout)
poll([{fd=3, events=POLLIN|POLLERR|POLLHUP|POLLNVAL}, {fd=5, events=POLLIN|
POLLERR|POLLHUP|POLLNVAL}], 2, 3000) = 0 (Timeout)
poll([{fd=3, events=POLLIN|POLLERR|POLLHUP|POLLNVAL}, {fd=5, events=POLLIN|
POLLERR|POLLHUP|POLLNVAL}], 2, 3000) = 0 (Timeout)
poll([{fd=3, events=POLLIN|POLLERR|POLLHUP|POLLNVAL}, {fd=5, events=POLLIN|
POLLERR|POLLHUP|POLLNVAL}], 2, 3000) = 0 (Timeout)
poll([{fd=3, events=POLLIN|POLLERR|POLLHUP|POLLNVAL}, {fd=5, events=POLLIN|
POLLERR|POLLHUP|POLLNVAL}], 2, 3000) = 0 (Timeout)
poll([{fd=3, events=POLLIN|POLLERR|POLLHUP|POLLNVAL}, {fd=5, events=POLLIN|
POLLERR|POLLHUP|POLLNVAL}], 2, 3000) = 0 (Timeout)
poll([{fd=3, events=POLLIN|POLLERR|POLLHUP|POLLNVAL}, {fd=5, events=POLLIN|
POLLERR|POLLHUP|POLLNVAL}], 2, 3000) = 0 (Timeout)
poll([{fd=3, events=POLLIN|POLLERR|POLLHUP|POLLNVAL}, {fd=5, events=POLLIN|
POLLERR|POLLHUP|POLLNVAL}], 2, 3000) = 0 (Timeout)
poll([{fd=3, events=POLLIN|POLLERR|POLLHUP|POLLNVAL}, {fd=5, events=POLLIN|
POLLERR|POLLHUP|POLLNVAL}], 2, 3000) = 0 (Timeout)
poll([{fd=3, events=POLLIN|POLLERR|POLLHUP|POLLNVAL}, {fd=5, events=POLLIN|
POLLERR|POLLHUP|POLLNVAL}], 2, 3000) = 0 (Timeout)
poll([{fd=3, events=POLLIN|POLLERR|POLLHUP|POLLNVAL}, {fd=5, events=POLLIN|
POLLERR|POLLHUP|POLLNVAL}], 2, 3000) = 0 (Timeout)
poll([{fd=3, events=POLLIN|POLLERR|POLLHUP|POLLNVAL}, {fd=5, events=POLLIN|
POLLERR|POLLHUP|POLLNVAL}], 2, 3000) = 0 (Timeout)
poll([{fd=3, events=POLLIN|POLLERR|POLLHUP|POLLNVAL}, {fd=5, events=POLLIN|
POLLERR|POLLHUP|POLLNVAL}], 2, 3000) = 0 (Timeout)
poll([{fd=3, events=POLLIN|POLLERR|POLLHUP|POLLNVAL}, {fd=5, events=POLLIN|
POLLERR|POLLHUP|POLLNVAL}], 2, 3000 <unfinished ...>

RE: [PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page

[Zhong, Xin]

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RE: [PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page

[Maria Wikström]

[-- Attachment #1: Type: text/plain, Size: 1348 bytes --]


Seems like my reply got eaten by the lists spam filter, so I resend with
attachment compressed. Should have thought of that :p


fre 2011-02-11 klockan 12:39 +0800 skrev Zhong, Xin:
> Hi,
> 
> Could you paste the output of sysrq+t here? Thanks!

Yes, it's in the attachment. I tried latest btrfs from git (last commit
Mon Feb 14 00:45:29 2011 +0000) but it hang so bad that I couldn't get
the output from sysrq+t to hit the disk. So the output is from vanilla
2.6.37 

// Maria

> -----Original Message-----
> From: Johannes Hirte [mailto:johannes.hirte@fem.tu-ilmenau.de] 
> Sent: Wednesday, February 02, 2011 7:35 AM
> To: Zhong, Xin
> Cc: Maria Wikström; linux-btrfs@vger.kernel.org
> Subject: Re: [PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page
> 
> On Friday 28 January 2011 04:53:24 Zhong, Xin wrote:
> > Could you describe the steps to recreate it?
> > It will be a great help for me to look further. Thanks!
> 
> It's a little strange. I have to systems with btrfs, both Gentoo-based. One is 
> affected by this bug the other is not. On the affected system it is enough to do 
> a 'emerge dev-libs/libgcrypt' that should normaly compile and install 
> libgcrypt. The emerge command is part of portage, the package management of 
> Gentoo. 
> The strace output looks similar to the one from Maria:
> 


[-- Attachment #2: vanilla_2.6.37_sysrq-t.txt.tar.gz --]
[-- Type: application/x-compressed-tar, Size: 22248 bytes --]

RE: [PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page

[Zhong, Xin]

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Re: [PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page

[Johannes Hirte]

[-- Attachment #1: Type: Text/Plain, Size: 610 bytes --]

On Friday 11 February 2011 05:39:39 Zhong, Xin wrote:
> Hi,
> 
> Could you paste the output of sysrq+t here? Thanks!

Sorry for the long delay. I've attached the dmesg output of sysrq-t from 
2.6.38-rc3 and rc4 as the behavior differs between both versions. With rc3 it 
don't need any interaction. I start 'emerge sys-devel/libgcrypt', the tasks 
hangs and top shows a svn process eating 100% CPU. With rc4 the system hangs 
too but the CPU load stays low. When I try to cancel the emerge process (ctrl 
c) the CPU load goes up and top shows the svn process together with a flush-
btrfs task, eating the CPU.

[-- Attachment #2: sysrq-t-38-rc.tar.bz2 --]
[-- Type: application/x-bzip-compressed-tar, Size: 45354 bytes --]

RE: [PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page

[Zhong, Xin]

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RE: [PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page

[Chris Mason]

Excerpts from Zhong, Xin's message of 2011-02-23 02:27:05 -0500:
> In the dmesg of rc4, I can see svn hang in shrink_dellalloc and there's two flush-btrfs threads hang there too.
> 
> Josef, it seems you are the expert in this area. Could you take a quick look? Thanks!

Ok, it does look like the fluhs-btrfs threads are busy trying to flush
things.

Could you please do a btrfs-show and a btrfs fi df /xxx (where xxx is
your mount point) and send the results here?

-chris

> 
> -----Original Message-----
> From: Johannes Hirte [mailto:johannes.hirte@fem.tu-ilmenau.de] 
> Sent: Wednesday, February 23, 2011 6:27 AM
> To: Zhong, Xin
> Cc: Maria Wikstr\xc3\xb6m; linux-btrfs@vger.kernel.org
> Subject: Re: [PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page
> 
> On Friday 11 February 2011 05:39:39 Zhong, Xin wrote:
> > Hi,
> > 
> > Could you paste the output of sysrq+t here? Thanks!
> 
> Sorry for the long delay. I've attached the dmesg output of sysrq-t from
> 2.6.38-rc3 and rc4 as the behavior differs between both versions. With rc3 it don't need any interaction. I start 'emerge sys-devel/libgcrypt', the tasks hangs and top shows a svn process eating 100% CPU. With rc4 the system hangs too but the CPU load stays low. When I try to cancel the emerge process (ctrl
> c) the CPU load goes up and top shows the svn process together with a flush- btrfs task, eating the CPU.
> \xff\xf4\xe8\xba{.n\xc7+\x89\xb7\x9f\xae\x89\xad\x86+%\x8a\xcb\xff\xb1\xe9\xdd\xb6\x17\xa5\x8aw\xff\xba{.n\xc7+\x89\xb7\xa5\x8a{\xb1\xfd\xbbk~\xcf\xe2\x9e\xd8^n\x87r\xa1\xf6\xa6z\xcb\x1a\x81\xebh\x99\xa8\xe8\xad\xda&\xa3\xfb\xe0z\xbf\xe4z\xb9\xde\x97\xfa+\x80\xca+zf\xa3\xa2\xb7h\x9a\x88\xa7~\x86\xad\x86\xdbi\xff\xff\xef\x81\xea\xff\x91\xea\xe7z_\xe8\xae\x0f\xe6j:+v\x89\xa8\xfe)\xdf\xa3\xf8m

Re: [PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page

[Johannes Hirte]

On Wednesday 23 February 2011 22:56:27 Chris Mason wrote:
> Excerpts from Zhong, Xin's message of 2011-02-23 02:27:05 -0500:
> > In the dmesg of rc4, I can see svn hang in shrink_dellalloc and there's
> > two flush-btrfs threads hang there too.
> > 
> > Josef, it seems you are the expert in this area. Could you take a quick
> > look? Thanks!
> 
> Ok, it does look like the fluhs-btrfs threads are busy trying to flush
> things.
> 
> Could you please do a btrfs-show and a btrfs fi df /xxx (where xxx is
> your mount point) and send the results here?
> 
> -chris

failed to read /dev/sr0
Label: none  uuid: 00eab15f-c4cf-4403-a529-9bc11fa50167
        Total devices 1 FS bytes used 47.72GB
        devid    1 size 65.69GB used 65.69GB path /dev/sda2

Label: none  uuid: c6f4e6e6-c4ba-4394-9e9c-bbc3d0b32793
        Total devices 1 FS bytes used 9.48GB
        devid    1 size 20.01GB used 20.01GB path /dev/sda1

Btrfs v0.19-35-g1b444cd-dirty

and btrfs fi df on

/

Data: total=15.49GB, used=8.35GB
System, DUP: total=8.00MB, used=12.00KB
System: total=4.00MB, used=0.00
Metadata, DUP: total=2.25GB, used=1.13GB

/home

Data: total=63.42GB, used=47.47GB
System: total=4.00MB, used=16.00KB
Metadata: total=2.27GB, used=251.34MB

The bug is reproducable on both filesystems.

regards,
  Johannes

RE: [PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page

[Maria Wikström]

[-- Attachment #1: Type: text/plain, Size: 2414 bytes --]

mån 2011-02-21 klockan 09:51 +0800 skrev Zhong, Xin:
> The backtrace in your attachment looks like a known bug of 2.6.37 which have already been fixed in 2.6.38. I have no idea why latest btrfs still hang in your environment if there's no debug info...
> 

Haha, yes that's very hard :)

2.6.38-rc6 and btrfs-unstable behaves the same way. I can close the
process with ctrl+c and it disappear a few seconds later. There is no
CPU usage. Reading works because I can start htop and watch "svn info"
disappear, but everything writing to btrfs slows down to a crawl. It
takes about 1 minute to log in. So I had to put the logs on an other
partition using ext3 to get the output from sysrq+t.

// Maria


> -----Original Message-----
> From: Maria Wikström [mailto:maria@ponstudios.se] 
> Sent: Friday, February 18, 2011 7:32 PM
> To: Zhong, Xin
> Cc: Johannes Hirte; linux-btrfs@vger.kernel.org
> Subject: RE: [PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page
> 
> 
> Seems like my reply got eaten by the lists spam filter, so I resend with attachment compressed. Should have thought of that :p
> 
> 
> fre 2011-02-11 klockan 12:39 +0800 skrev Zhong, Xin:
> > Hi,
> > 
> > Could you paste the output of sysrq+t here? Thanks!
> 
> Yes, it's in the attachment. I tried latest btrfs from git (last commit Mon Feb 14 00:45:29 2011 +0000) but it hang so bad that I couldn't get the output from sysrq+t to hit the disk. So the output is from vanilla
> 2.6.37 
> 
> // Maria
> 
> > -----Original Message-----
> > From: Johannes Hirte [mailto:johannes.hirte@fem.tu-ilmenau.de]
> > Sent: Wednesday, February 02, 2011 7:35 AM
> > To: Zhong, Xin
> > Cc: Maria Wikström; linux-btrfs@vger.kernel.org
> > Subject: Re: [PATCH v2]Btrfs: pwrite blocked when writing from the 
> > mmaped buffer of the same page
> > 
> > On Friday 28 January 2011 04:53:24 Zhong, Xin wrote:
> > > Could you describe the steps to recreate it?
> > > It will be a great help for me to look further. Thanks!
> > 
> > It's a little strange. I have to systems with btrfs, both 
> > Gentoo-based. One is affected by this bug the other is not. On the 
> > affected system it is enough to do a 'emerge dev-libs/libgcrypt' that 
> > should normaly compile and install libgcrypt. The emerge command is 
> > part of portage, the package management of Gentoo.
> > The strace output looks similar to the one from Maria:
> > 
> 


[-- Attachment #2: 2.6.38-rc6_sysrq-t.txt.tar.bz2 --]
[-- Type: application/x-bzip-compressed-tar, Size: 17699 bytes --]

[-- Attachment #3: btrfs-unstable_sysrq-t.txt.tar.bz2 --]
[-- Type: application/x-bzip-compressed-tar, Size: 15788 bytes --]

Re: [PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page

[Chris Mason]

Excerpts from Johannes Hirte's message of 2011-02-23 18:02:44 -0500:
> On Wednesday 23 February 2011 22:56:27 Chris Mason wrote:
> > Excerpts from Zhong, Xin's message of 2011-02-23 02:27:05 -0500:
> > > In the dmesg of rc4, I can see svn hang in shrink_dellalloc and there's
> > > two flush-btrfs threads hang there too.
> > > 
> > > Josef, it seems you are the expert in this area. Could you take a quick
> > > look? Thanks!
> > 
> > Ok, it does look like the fluhs-btrfs threads are busy trying to flush
> > things.
> > 
> > Could you please do a btrfs-show and a btrfs fi df /xxx (where xxx is
> > your mount point) and send the results here?
> > 
> > -chris
> 
> failed to read /dev/sr0
> Label: none  uuid: 00eab15f-c4cf-4403-a529-9bc11fa50167
>         Total devices 1 FS bytes used 47.72GB
>         devid    1 size 65.69GB used 65.69GB path /dev/sda2
> 
> Label: none  uuid: c6f4e6e6-c4ba-4394-9e9c-bbc3d0b32793
>         Total devices 1 FS bytes used 9.48GB
>         devid    1 size 20.01GB used 20.01GB path /dev/sda1
> 
> Btrfs v0.19-35-g1b444cd-dirty
> 
> and btrfs fi df on
> 
> /
> 
> Data: total=15.49GB, used=8.35GB
> System, DUP: total=8.00MB, used=12.00KB
> System: total=4.00MB, used=0.00
> Metadata, DUP: total=2.25GB, used=1.13GB
> 
> /home
> 
> Data: total=63.42GB, used=47.47GB
> System: total=4.00MB, used=16.00KB
> Metadata: total=2.27GB, used=251.34MB
> 
> The bug is reproducable on both filesystems.

Ok, you've got a good amount of metadata space free, but it is
frantically trying to make room for the delayed allocation.  Let me see
if I can recreate this setup here.

-chris

Re: [PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page

[Mitch Harder]

2011/2/24 Maria Wikstr=F6m <maria@ponstudios.se>:
> m=E5n 2011-02-21 klockan 09:51 +0800 skrev Zhong, Xin:
>> The backtrace in your attachment looks like a known bug of 2.6.37 wh=
ich have already been fixed in 2.6.38. I have no idea why latest btrfs =
still hang in your environment if there's no debug info...
>>
>
> Haha, yes that's very hard :)
>
> 2.6.38-rc6 and btrfs-unstable behaves the same way. I can close the
> process with ctrl+c and it disappear a few seconds later. There is no
> CPU usage. Reading works because I can start htop and watch "svn info=
"
> disappear, but everything writing to btrfs slows down to a crawl. It
> takes about 1 minute to log in. So I had to put the logs on an other
> partition using ext3 to get the output from sysrq+t.
>

I believe I've been experiencing this issue also.  However, my problem
usually results in a "No space left on device" error rather than a
lock-up or crash.  But I've bisected my issue to this patch, and my
"btrfs fi show" and "btrfs fi df" looks similar to others who've
posted to this tread with all my space being allocated, but not used.

I've been playing around with ftrace to try to get some information on
the issue.  Since I'm getting a soft error, I can used a command like
"echo 1 > tracing_on; emerge -1av openmotif; echo 0 > tracing_on" to
end the trace as soon as the build fails.

The traces are probably too large for the M/L (~275kb compressed), so
I've put them up on my local server in case anybody can find them
useful:

http://dontpanic.dyndns.org/emerge-openmotif-ftrace.gz

I'm still only capturing the tail end of the problem, but maybe
someone will find these insightful.

Let me know if you want me to increase the ftrace buffer size or
insert some trace_printk debugging statements.
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Re: [PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page

[Chris Mason]

Excerpts from Mitch Harder's message of 2011-02-24 10:55:15 -0500:
> 2011/2/24 Maria Wikstr=C3=B6m <maria@ponstudios.se>:
> > m=C3=A5n 2011-02-21 klockan 09:51 +0800 skrev Zhong, Xin:
> >> The backtrace in your attachment looks like a known bug of 2.6.37 =
which have already been fixed in 2.6.38. I have no idea why latest btrf=
s still hang in your environment if there's no debug info...
> >>
> >
> > Haha, yes that's very hard :)
> >
> > 2.6.38-rc6 and btrfs-unstable behaves the same way. I can close the
> > process with ctrl+c and it disappear a few seconds later. There is =
no
> > CPU usage. Reading works because I can start htop and watch "svn in=
fo"
> > disappear, but everything writing to btrfs slows down to a crawl. I=
t
> > takes about 1 minute to log in. So I had to put the logs on an othe=
r
> > partition using ext3 to get the output from sysrq+t.
> >
>=20
> I believe I've been experiencing this issue also.  However, my proble=
m
> usually results in a "No space left on device" error rather than a
> lock-up or crash.  But I've bisected my issue to this patch, and my
> "btrfs fi show" and "btrfs fi df" looks similar to others who've
> posted to this tread with all my space being allocated, but not used.
>=20

Sorry, which patch did you bisect the problem down to?

> I've been playing around with ftrace to try to get some information o=
n
> the issue.  Since I'm getting a soft error, I can used a command like
> "echo 1 > tracing_on; emerge -1av openmotif; echo 0 > tracing_on" to
> end the trace as soon as the build fails.
>=20
> The traces are probably too large for the M/L (~275kb compressed), so
> I've put them up on my local server in case anybody can find them
> useful:
>=20
> http://dontpanic.dyndns.org/emerge-openmotif-ftrace.gz
>=20
> I'm still only capturing the tail end of the problem, but maybe
> someone will find these insightful.
>=20
> Let me know if you want me to increase the ftrace buffer size or
> insert some trace_printk debugging statements.

Thanks, I'll take a look.

-chris
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Re: [PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page

[Mitch Harder]

On Thu, Feb 24, 2011 at 10:00 AM, Chris Mason <chris.mason@oracle.com> =
wrote:
> Excerpts from Mitch Harder's message of 2011-02-24 10:55:15 -0500:
>> 2011/2/24 Maria Wikstr=F6m <maria@ponstudios.se>:
>> > m=E5n 2011-02-21 klockan 09:51 +0800 skrev Zhong, Xin:
>> >> The backtrace in your attachment looks like a known bug of 2.6.37=
 which have already been fixed in 2.6.38. I have no idea why latest btr=
fs still hang in your environment if there's no debug info...
>> >>
>> >
>> > Haha, yes that's very hard :)
>> >
>> > 2.6.38-rc6 and btrfs-unstable behaves the same way. I can close th=
e
>> > process with ctrl+c and it disappear a few seconds later. There is=
 no
>> > CPU usage. Reading works because I can start htop and watch "svn i=
nfo"
>> > disappear, but everything writing to btrfs slows down to a crawl. =
It
>> > takes about 1 minute to log in. So I had to put the logs on an oth=
er
>> > partition using ext3 to get the output from sysrq+t.
>> >
>>
>> I believe I've been experiencing this issue also. =A0However, my pro=
blem
>> usually results in a "No space left on device" error rather than a
>> lock-up or crash. =A0But I've bisected my issue to this patch, and m=
y
>> "btrfs fi show" and "btrfs fi df" looks similar to others who've
>> posted to this tread with all my space being allocated, but not used=
=2E
>>
>
> Sorry, which patch did you bisect the problem down to?
>

The patch at the head of this thread:

Btrfs: pwrite blocked when writing from the mmaped buffer of the same p=
age
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Re: [PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page

[Chris Mason]

Excerpts from Mitch Harder's message of 2011-02-24 11:03:07 -0500:
> On Thu, Feb 24, 2011 at 10:00 AM, Chris Mason <chris.mason@oracle.com=
> wrote:
> > Excerpts from Mitch Harder's message of 2011-02-24 10:55:15 -0500:
> >> 2011/2/24 Maria Wikstr=C3=B6m <maria@ponstudios.se>:
> >> > m=C3=A5n 2011-02-21 klockan 09:51 +0800 skrev Zhong, Xin:
> >> >> The backtrace in your attachment looks like a known bug of 2.6.=
37 which have already been fixed in 2.6.38. I have no idea why latest b=
trfs still hang in your environment if there's no debug info...
> >> >>
> >> >
> >> > Haha, yes that's very hard :)
> >> >
> >> > 2.6.38-rc6 and btrfs-unstable behaves the same way. I can close =
the
> >> > process with ctrl+c and it disappear a few seconds later. There =
is no
> >> > CPU usage. Reading works because I can start htop and watch "svn=
 info"
> >> > disappear, but everything writing to btrfs slows down to a crawl=
=2E It
> >> > takes about 1 minute to log in. So I had to put the logs on an o=
ther
> >> > partition using ext3 to get the output from sysrq+t.
> >> >
> >>
> >> I believe I've been experiencing this issue also. =C2=A0However, m=
y problem
> >> usually results in a "No space left on device" error rather than a
> >> lock-up or crash. =C2=A0But I've bisected my issue to this patch, =
and my
> >> "btrfs fi show" and "btrfs fi df" looks similar to others who've
> >> posted to this tread with all my space being allocated, but not us=
ed.
> >>
> >
> > Sorry, which patch did you bisect the problem down to?
> >
>=20
> The patch at the head of this thread:
>=20
> Btrfs: pwrite blocked when writing from the mmaped buffer of the same=
 page

Hmmm, that patch shouldn't be changing our performance under delalloc
pressure, and it really shouldn't impact early enospc.

-chris
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Re: [PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page

[Mitch Harder]

On Thu, Feb 24, 2011 at 10:19 AM, Chris Mason <chris.mason@oracle.com> =
wrote:
> Excerpts from Mitch Harder's message of 2011-02-24 11:03:07 -0500:
>> On Thu, Feb 24, 2011 at 10:00 AM, Chris Mason <chris.mason@oracle.co=
m> wrote:
>> > Excerpts from Mitch Harder's message of 2011-02-24 10:55:15 -0500:
>> >> 2011/2/24 Maria Wikstr=F6m <maria@ponstudios.se>:
>> >> > m=E5n 2011-02-21 klockan 09:51 +0800 skrev Zhong, Xin:
>> >> >> The backtrace in your attachment looks like a known bug of 2.6=
=2E37 which have already been fixed in 2.6.38. I have no idea why lates=
t btrfs still hang in your environment if there's no debug info...
>> >> >>
>> >> >
>> >> > Haha, yes that's very hard :)
>> >> >
>> >> > 2.6.38-rc6 and btrfs-unstable behaves the same way. I can close=
 the
>> >> > process with ctrl+c and it disappear a few seconds later. There=
 is no
>> >> > CPU usage. Reading works because I can start htop and watch "sv=
n info"
>> >> > disappear, but everything writing to btrfs slows down to a craw=
l. It
>> >> > takes about 1 minute to log in. So I had to put the logs on an =
other
>> >> > partition using ext3 to get the output from sysrq+t.
>> >> >
>> >>
>> >> I believe I've been experiencing this issue also. =A0However, my =
problem
>> >> usually results in a "No space left on device" error rather than =
a
>> >> lock-up or crash. =A0But I've bisected my issue to this patch, an=
d my
>> >> "btrfs fi show" and "btrfs fi df" looks similar to others who've
>> >> posted to this tread with all my space being allocated, but not u=
sed.
>> >>
>> >
>> > Sorry, which patch did you bisect the problem down to?
>> >
>>
>> The patch at the head of this thread:
>>
>> Btrfs: pwrite blocked when writing from the mmaped buffer of the sam=
e page
>
> Hmmm, that patch shouldn't be changing our performance under delalloc
> pressure, and it really shouldn't impact early enospc.
>

I've bisected this issue around where this patch went into git, and
I've also constructed a testing patch that reverts this patch, and
placed it on top of the current Btrfs git sources (I understand this
patch addresses a real issue, this was just for testing).

It could be that this patch just "uncovers" another problem, but all
my tests seem to point to this patch triggering this issue.
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Re: [PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page

[Piotr Szymaniak]

[-- Attachment #1.1: Type: text/plain, Size: 2887 bytes --]

On Mon, Feb 21, 2011 at 09:51:11AM +0800, Zhong, Xin wrote:
> The backtrace in your attachment looks like a known bug of 2.6.37 which have already been fixed in 2.6.38. I have no idea why latest btrfs still hang in your environment if there's no debug info...

Hi list.

I'm watching this list for a while because it seems, that I'm also
affected by this bug. In the archives I found someone with Gentoo system
with freezing `svn info' (thats why I joined). Well, seems that I have 
same issue here.

Attached latest _rc kernel sysrq+t output (first part when the `svn
info' freezed on libgcrypt, and second after ctrl+c that emerge).

Seems that my backtrace is small compared to Marias. I'm missing some
features in kernel to get larger backtraces?

Piotr Szymaniak.



> -----Original Message-----
> From: Maria Wikström [mailto:maria@ponstudios.se] 
> Sent: Friday, February 18, 2011 7:32 PM
> To: Zhong, Xin
> Cc: Johannes Hirte; linux-btrfs@vger.kernel.org
> Subject: RE: [PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page
> 
> 
> Seems like my reply got eaten by the lists spam filter, so I resend with attachment compressed. Should have thought of that :p
> 
> 
> fre 2011-02-11 klockan 12:39 +0800 skrev Zhong, Xin:
> > Hi,
> > 
> > Could you paste the output of sysrq+t here? Thanks!
> 
> Yes, it's in the attachment. I tried latest btrfs from git (last commit Mon Feb 14 00:45:29 2011 +0000) but it hang so bad that I couldn't get the output from sysrq+t to hit the disk. So the output is from vanilla
> 2.6.37 
> 
> // Maria
> 
> > -----Original Message-----
> > From: Johannes Hirte [mailto:johannes.hirte@fem.tu-ilmenau.de]
> > Sent: Wednesday, February 02, 2011 7:35 AM
> > To: Zhong, Xin
> > Cc: Maria Wikström; linux-btrfs@vger.kernel.org
> > Subject: Re: [PATCH v2]Btrfs: pwrite blocked when writing from the 
> > mmaped buffer of the same page
> > 
> > On Friday 28 January 2011 04:53:24 Zhong, Xin wrote:
> > > Could you describe the steps to recreate it?
> > > It will be a great help for me to look further. Thanks!
> > 
> > It's a little strange. I have to systems with btrfs, both 
> > Gentoo-based. One is affected by this bug the other is not. On the 
> > affected system it is enough to do a 'emerge dev-libs/libgcrypt' that 
> > should normaly compile and install libgcrypt. The emerge command is 
> > part of portage, the package management of Gentoo.
> > The strace output looks similar to the one from Maria:
> > 
> 
> N?????r??y????b?X??ǧv?^?)޺{.n?+????{?n?߲)????w*\x1fjg???\x1e?????ݢj/???z?ޖ??2?ޙ????&?)ߡ?a??\x7f??\x1e?G???h?\x0f?j:+v???w??٥

-- 
Druzyna  futbolowa  tutaj  jest  do  niczego, ale ucze sie troche pilki
noznej.  Trener  mowi,  ze  pilka nozna to futbol dla inteligentnych, a
futbol to futbol dla kretynow.
  -- Stephen King, "The Dead Zone"

[-- Attachment #1.2: vanilla-2.6.38-rc6_sysrq-t.bz2 --]
[-- Type: application/x-bzip2, Size: 4837 bytes --]

[-- Attachment #2: Type: application/pgp-signature, Size: 198 bytes --]

Re: [PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page

[Mitch Harder]

On Thu, Feb 24, 2011 at 5:14 PM, Mitch Harder
<mitch.harder@sabayonlinux.org> wrote:
> On Thu, Feb 24, 2011 at 10:32 AM, Mitch Harder
> <mitch.harder@sabayonlinux.org> wrote:
>> On Thu, Feb 24, 2011 at 10:19 AM, Chris Mason <chris.mason@oracle.co=
m> wrote:
>>> Excerpts from Mitch Harder's message of 2011-02-24 11:03:07 -0500:
>>>> On Thu, Feb 24, 2011 at 10:00 AM, Chris Mason <chris.mason@oracle.=
com> wrote:
>>>> > Excerpts from Mitch Harder's message of 2011-02-24 10:55:15 -050=
0:
>>>> >> 2011/2/24 Maria Wikstr=F6m <maria@ponstudios.se>:
>>>> >> > m=E5n 2011-02-21 klockan 09:51 +0800 skrev Zhong, Xin:
>>>> >> >> The backtrace in your attachment looks like a known bug of 2=
=2E6.37 which have already been fixed in 2.6.38. I have no idea why lat=
est btrfs still hang in your environment if there's no debug info...
>>>> >> >>
>>>> >> >
>>>> >> > Haha, yes that's very hard :)
>>>> >> >
>>>> >> > 2.6.38-rc6 and btrfs-unstable behaves the same way. I can clo=
se the
>>>> >> > process with ctrl+c and it disappear a few seconds later. The=
re is no
>>>> >> > CPU usage. Reading works because I can start htop and watch "=
svn info"
>>>> >> > disappear, but everything writing to btrfs slows down to a cr=
awl. It
>>>> >> > takes about 1 minute to log in. So I had to put the logs on a=
n other
>>>> >> > partition using ext3 to get the output from sysrq+t.
>>>> >> >
>>>> >>
>>>> >> I believe I've been experiencing this issue also. =A0However, m=
y problem
>>>> >> usually results in a "No space left on device" error rather tha=
n a
>>>> >> lock-up or crash. =A0But I've bisected my issue to this patch, =
and my
>>>> >> "btrfs fi show" and "btrfs fi df" looks similar to others who'v=
e
>>>> >> posted to this tread with all my space being allocated, but not=
 used.
>>>> >>
>>>> >
>>>> > Sorry, which patch did you bisect the problem down to?
>>>> >
>>>>
>>>> The patch at the head of this thread:
>>>>
>>>> Btrfs: pwrite blocked when writing from the mmaped buffer of the s=
ame page
>>>
>>> Hmmm, that patch shouldn't be changing our performance under delall=
oc
>>> pressure, and it really shouldn't impact early enospc.
>>>
>>
>> I've bisected this issue around where this patch went into git, and
>> I've also constructed a testing patch that reverts this patch, and
>> placed it on top of the current Btrfs git sources (I understand this
>> patch addresses a real issue, this was just for testing).
>>
>> It could be that this patch just "uncovers" another problem, but all
>> my tests seem to point to this patch triggering this issue.
>>
>
> I don't belief the previous ftrace I supplied had a large enough scop=
e
> to capture the issue.
>
> I've expanded my ftrace buffer, and filtered out everything but btrfs=
*
> function calls ("# echo btrfs* >
> /sys/kernel/debug/tracing/set_ftrace_filter").
>
> In this trace, I see btrfs spending a great deal of time in a while
> loop (while (iov_iter_count(&i) > 0) {)) in the btrfs_file_aio_write(=
)
> function in file.c without exiting the function.
>
> I'm going to try to inject some debugging trace_printk() statements t=
o
> find if that portion of code is proceeding normally with my test case=
=2E
>
> I've put my expanded trace up on my local server, but my upload
> bandwidth is pretty sad, and it may take a few minutes to transfer
> even though it's only a 6MB file.
>
> http://dontpanic.dyndns.org/trace-openmotif-btrfs-v3.gz
>

Apologies for only hitting "Reply" instead of "Reply-All" on my last me=
ssage.

I've inserted additional trace_printk() to the btrfs_file_aio_write()
and btrfs_copy_from_user() function in file.c in order to characterize
the problem I've been encountering.

I can see btrfs getting stuck in a loop in the "while
(iov_iter_count(&i) > 0) {}" portion of the btrfs_file_aio_write()
function.

The loop is more-or-less following this process (from within the
"while (iov_iter_count(&i) > 0) {}" loop):

(1) Reserve some space with btrfs_delalloc_reserve_space()
(2) Prepare the reserved space with prepare_pages()
(3) Call btrfs_copy_from_user() to copy to the prepared space.
-------------> From btrfs_copy_from_user()
(4) ........Try to copy with copied =3D iov_iter_copy_from_user_atomic(=
)
(5) ........The above operation results with copied =3D=3D 0. Break and
return with a return value of 0 bytes copied.
(6) There is no special handling for copied =3D=3D 0 in the "while
(iov_iter_count(&i) > 0) {}" loop, so it loops back around, reserves
some more space, and tries again.

If I look back at how the code was set up before the patch at the head
of this thread was applied (Btrfs: pwrite blocked when writing from
the mmaped buffer of the same page), the btrfs_copy_from_user()
function had some handling for "copied =3D=3D 0" that would change the
scope of the amount to write, and loop back to try the write again.

I attempted to construct a patch that just reverted the handling for
"copied =3D=3D 0" in btrfs_copy_from_user(), however, that just resulte=
d
in my computer locking up when it reached the point where it was
previously beginning to allocate disk space.

So, I apologize for not having a patch to address the issue I'm
seeing, but I hope I've added some insight.
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Re: [PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page

[Mitch Harder]

On Fri, Feb 25, 2011 at 11:11 AM, Mitch Harder
<mitch.harder@sabayonlinux.org> wrote:
> On Thu, Feb 24, 2011 at 5:14 PM, Mitch Harder
> <mitch.harder@sabayonlinux.org> wrote:
>> On Thu, Feb 24, 2011 at 10:32 AM, Mitch Harder
>> <mitch.harder@sabayonlinux.org> wrote:
>>> On Thu, Feb 24, 2011 at 10:19 AM, Chris Mason <chris.mason@oracle.c=
om> wrote:
>>>> Excerpts from Mitch Harder's message of 2011-02-24 11:03:07 -0500:
>>>>> On Thu, Feb 24, 2011 at 10:00 AM, Chris Mason <chris.mason@oracle=
=2Ecom> wrote:
>>>>> > Excerpts from Mitch Harder's message of 2011-02-24 10:55:15 -05=
00:
>>>>> >> 2011/2/24 Maria Wikstr=F6m <maria@ponstudios.se>:
>>>>> >> > m=E5n 2011-02-21 klockan 09:51 +0800 skrev Zhong, Xin:
>>>>> >> >> The backtrace in your attachment looks like a known bug of =
2.6.37 which have already been fixed in 2.6.38. I have no idea why late=
st btrfs still hang in your environment if there's no debug info...
>>>>> >> >>
>>>>> >> >
>>>>> >> > Haha, yes that's very hard :)
>>>>> >> >
>>>>> >> > 2.6.38-rc6 and btrfs-unstable behaves the same way. I can cl=
ose the
>>>>> >> > process with ctrl+c and it disappear a few seconds later. Th=
ere is no
>>>>> >> > CPU usage. Reading works because I can start htop and watch =
"svn info"
>>>>> >> > disappear, but everything writing to btrfs slows down to a c=
rawl. It
>>>>> >> > takes about 1 minute to log in. So I had to put the logs on =
an other
>>>>> >> > partition using ext3 to get the output from sysrq+t.
>>>>> >> >
>>>>> >>
>>>>> >> I believe I've been experiencing this issue also. =A0However, =
my problem
>>>>> >> usually results in a "No space left on device" error rather th=
an a
>>>>> >> lock-up or crash. =A0But I've bisected my issue to this patch,=
 and my
>>>>> >> "btrfs fi show" and "btrfs fi df" looks similar to others who'=
ve
>>>>> >> posted to this tread with all my space being allocated, but no=
t used.
>>>>> >>
>>>>> >
>>>>> > Sorry, which patch did you bisect the problem down to?
>>>>> >
>>>>>
>>>>> The patch at the head of this thread:
>>>>>
>>>>> Btrfs: pwrite blocked when writing from the mmaped buffer of the =
same page
>>>>
>>>> Hmmm, that patch shouldn't be changing our performance under delal=
loc
>>>> pressure, and it really shouldn't impact early enospc.
>>>>
>>>
>>> I've bisected this issue around where this patch went into git, and
>>> I've also constructed a testing patch that reverts this patch, and
>>> placed it on top of the current Btrfs git sources (I understand thi=
s
>>> patch addresses a real issue, this was just for testing).
>>>
>>> It could be that this patch just "uncovers" another problem, but al=
l
>>> my tests seem to point to this patch triggering this issue.
>>>
>>
>> I don't belief the previous ftrace I supplied had a large enough sco=
pe
>> to capture the issue.
>>
>> I've expanded my ftrace buffer, and filtered out everything but btrf=
s*
>> function calls ("# echo btrfs* >
>> /sys/kernel/debug/tracing/set_ftrace_filter").
>>
>> In this trace, I see btrfs spending a great deal of time in a while
>> loop (while (iov_iter_count(&i) > 0) {)) in the btrfs_file_aio_write=
()
>> function in file.c without exiting the function.
>>
>> I'm going to try to inject some debugging trace_printk() statements =
to
>> find if that portion of code is proceeding normally with my test cas=
e.
>>
>> I've put my expanded trace up on my local server, but my upload
>> bandwidth is pretty sad, and it may take a few minutes to transfer
>> even though it's only a 6MB file.
>>
>> http://dontpanic.dyndns.org/trace-openmotif-btrfs-v3.gz
>>
>
> Apologies for only hitting "Reply" instead of "Reply-All" on my last =
message.
>
> I've inserted additional trace_printk() to the btrfs_file_aio_write()
> and btrfs_copy_from_user() function in file.c in order to characteriz=
e
> the problem I've been encountering.
>
> I can see btrfs getting stuck in a loop in the "while
> (iov_iter_count(&i) > 0) {}" portion of the btrfs_file_aio_write()
> function.
>
> The loop is more-or-less following this process (from within the
> "while (iov_iter_count(&i) > 0) {}" loop):
>
> (1) Reserve some space with btrfs_delalloc_reserve_space()
> (2) Prepare the reserved space with prepare_pages()
> (3) Call btrfs_copy_from_user() to copy to the prepared space.
> -------------> From btrfs_copy_from_user()
> (4) ........Try to copy with copied =3D iov_iter_copy_from_user_atomi=
c()
> (5) ........The above operation results with copied =3D=3D 0. Break a=
nd
> return with a return value of 0 bytes copied.
> (6) There is no special handling for copied =3D=3D 0 in the "while
> (iov_iter_count(&i) > 0) {}" loop, so it loops back around, reserves
> some more space, and tries again.
>
> If I look back at how the code was set up before the patch at the hea=
d
> of this thread was applied (Btrfs: pwrite blocked when writing from
> the mmaped buffer of the same page), the btrfs_copy_from_user()
> function had some handling for "copied =3D=3D 0" that would change th=
e
> scope of the amount to write, and loop back to try the write again.
>
> I attempted to construct a patch that just reverted the handling for
> "copied =3D=3D 0" in btrfs_copy_from_user(), however, that just resul=
ted
> in my computer locking up when it reached the point where it was
> previously beginning to allocate disk space.
>
> So, I apologize for not having a patch to address the issue I'm
> seeing, but I hope I've added some insight.
>

Some clarification on my previous message...

After looking at my ftrace log more closely, I can see where Btrfs is
trying to release the allocated pages.  However, the calculation for
the number of dirty_pages is equal to 1 when "copied =3D=3D 0".

So I'm seeing at least two problems:
(1)  It keeps looping when "copied =3D=3D 0".
(2)  One dirty page is not being released on every loop even though
"copied =3D=3D 0" (at least this problem keeps it from being an infinit=
e
loop by eventually exhausting reserveable space on the disk).
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Re: [PATCH v2]Btrfs: pwrite blocked when writing from the mmaped buffer of the same page

[Chris Mason]

Excerpts from Mitch Harder's message of 2011-02-25 13:43:37 -0500:
> > The loop is more-or-less following this process (from within the
> > "while (iov_iter_count(&i) > 0) {}" loop):
> >
> > (1) Reserve some space with btrfs_delalloc_reserve_space()
> > (2) Prepare the reserved space with prepare_pages()
> > (3) Call btrfs_copy_from_user() to copy to the prepared space.
> > -------------> From btrfs_copy_from_user()
> > (4) ........Try to copy with copied = iov_iter_copy_from_user_atomic()
> > (5) ........The above operation results with copied == 0. Break and
> > return with a return value of 0 bytes copied.
> > (6) There is no special handling for copied == 0 in the "while
> > (iov_iter_count(&i) > 0) {}" loop, so it loops back around, reserves
> > some more space, and tries again.
> >
> > If I look back at how the code was set up before the patch at the head
> > of this thread was applied (Btrfs: pwrite blocked when writing from
> > the mmaped buffer of the same page), the btrfs_copy_from_user()
> > function had some handling for "copied == 0" that would change the
> > scope of the amount to write, and loop back to try the write again.
> >
> > I attempted to construct a patch that just reverted the handling for
> > "copied == 0" in btrfs_copy_from_user(), however, that just resulted
> > in my computer locking up when it reached the point where it was
> > previously beginning to allocate disk space.
> >
> > So, I apologize for not having a patch to address the issue I'm
> > seeing, but I hope I've added some insight.
> >
> 
> Some clarification on my previous message...
> 
> After looking at my ftrace log more closely, I can see where Btrfs is
> trying to release the allocated pages.  However, the calculation for
> the number of dirty_pages is equal to 1 when "copied == 0".
> 
> So I'm seeing at least two problems:
> (1)  It keeps looping when "copied == 0".
> (2)  One dirty page is not being released on every loop even though
> "copied == 0" (at least this problem keeps it from being an infinite
> loop by eventually exhausting reserveable space on the disk).

Very nice, I think you're exactly right.  I should be able to reproduce this
now, thanks!

-chris

[PATCH] btrfs file write debugging patch

[Chris Mason]

Excerpts from Mitch Harder's message of 2011-02-25 13:43:37 -0500:
> Some clarification on my previous message...
> 
> After looking at my ftrace log more closely, I can see where Btrfs is
> trying to release the allocated pages.  However, the calculation for
> the number of dirty_pages is equal to 1 when "copied == 0".
> 
> So I'm seeing at least two problems:
> (1)  It keeps looping when "copied == 0".
> (2)  One dirty page is not being released on every loop even though
> "copied == 0" (at least this problem keeps it from being an infinite
> loop by eventually exhausting reserveable space on the disk).

Hi everyone,

There are actually tow bugs here.  First the one that Mitch hit, and a
second one that still results in bad file_write results with my
debugging hunks (the first two hunks below) in place.

My patch fixes Mitch's bug by checking for copied == 0 after
btrfs_copy_from_user and going the correct delalloc accounting.  This
one looks solved, but you'll notice the patch is bigger.

First, I add some random failures to btrfs_copy_from_user() by failing
everyone once and a while.  This was much more reliable than trying to
use memory pressure than making copy_from_user fail.

If copy_from_user fails and we partially update a page, we end up with a
page that may go away due to memory pressure.  But, btrfs_file_write
assumes that only the first and last page may have good data that needs
to be read off the disk.

This patch ditches that code and puts it into prepare_pages instead.
But I'm still having some errors during long stress.sh runs.  Ideas are
more than welcome, hopefully some other timezones will kick in ideas
while I sleep.

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 7084140..89a6a26 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -54,6 +54,13 @@ static noinline int btrfs_copy_from_user(loff_t pos, int num_pages,
 	int offset = pos & (PAGE_CACHE_SIZE - 1);
 	int total_copied = 0;
 
+	if ((jiffies % 10) == 0)
+		return 0;
+
+	if ((jiffies % 25) == 0) {
+		write_bytes /= 2;
+	}
+
 	while (write_bytes > 0) {
 		size_t count = min_t(size_t,
 				     PAGE_CACHE_SIZE - offset, write_bytes);
@@ -763,6 +770,26 @@ out:
 }
 
 /*
+ * on error we return an unlocked page and the error value
+ * on success we return a locked page and 0
+ */
+static int prepare_uptodate_page(struct page *page, u64 pos)
+{
+	int ret = 0;
+	if ((pos & (PAGE_CACHE_SIZE - 1)) && !PageUptodate(page)) {
+		ret = btrfs_readpage(NULL, page);
+		if (ret)
+			return ret;
+		lock_page(page);
+		if (!PageUptodate(page)) {
+			unlock_page(page);
+			return -EIO;
+		}
+	}
+	return 0;
+}
+
+/*
  * this gets pages into the page cache and locks them down, it also properly
  * waits for data=ordered extents to finish before allowing the pages to be
  * modified.
@@ -777,6 +804,7 @@ static noinline int prepare_pages(struct btrfs_root *root, struct file *file,
 	unsigned long index = pos >> PAGE_CACHE_SHIFT;
 	struct inode *inode = fdentry(file)->d_inode;
 	int err = 0;
+	int faili = 0;
 	u64 start_pos;
 	u64 last_pos;
 
@@ -794,15 +822,24 @@ again:
 	for (i = 0; i < num_pages; i++) {
 		pages[i] = grab_cache_page(inode->i_mapping, index + i);
 		if (!pages[i]) {
-			int c;
-			for (c = i - 1; c >= 0; c--) {
-				unlock_page(pages[c]);
-				page_cache_release(pages[c]);
-			}
-			return -ENOMEM;
+			faili = i - 1;
+			err = -ENOMEM;
+			goto fail;
+		}
+
+		if (i == 0)
+			err = prepare_uptodate_page(pages[i], pos);
+		else if (i == num_pages - 1)
+			err = prepare_uptodate_page(pages[i],
+						    pos + write_bytes);
+		if (err) {
+			page_cache_release(pages[i]);
+			faili = i - 1;
+			goto fail;
 		}
 		wait_on_page_writeback(pages[i]);
 	}
+	err = 0;
 	if (start_pos < inode->i_size) {
 		struct btrfs_ordered_extent *ordered;
 		lock_extent_bits(&BTRFS_I(inode)->io_tree,
@@ -842,6 +879,14 @@ again:
 		WARN_ON(!PageLocked(pages[i]));
 	}
 	return 0;
+fail:
+	while (faili >= 0) {
+		unlock_page(pages[faili]);
+		page_cache_release(pages[faili]);
+		faili--;
+	}
+	return err;
+
 }
 
 static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
@@ -851,7 +896,6 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
 	struct file *file = iocb->ki_filp;
 	struct inode *inode = fdentry(file)->d_inode;
 	struct btrfs_root *root = BTRFS_I(inode)->root;
-	struct page *pinned[2];
 	struct page **pages = NULL;
 	struct iov_iter i;
 	loff_t *ppos = &iocb->ki_pos;
@@ -872,9 +916,6 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
 	will_write = ((file->f_flags & O_DSYNC) || IS_SYNC(inode) ||
 		      (file->f_flags & O_DIRECT));
 
-	pinned[0] = NULL;
-	pinned[1] = NULL;
-
 	start_pos = pos;
 
 	vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);
@@ -962,32 +1003,6 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
 	first_index = pos >> PAGE_CACHE_SHIFT;
 	last_index = (pos + iov_iter_count(&i)) >> PAGE_CACHE_SHIFT;
 
-	/*
-	 * there are lots of better ways to do this, but this code
-	 * makes sure the first and last page in the file range are
-	 * up to date and ready for cow
-	 */
-	if ((pos & (PAGE_CACHE_SIZE - 1))) {
-		pinned[0] = grab_cache_page(inode->i_mapping, first_index);
-		if (!PageUptodate(pinned[0])) {
-			ret = btrfs_readpage(NULL, pinned[0]);
-			BUG_ON(ret);
-			wait_on_page_locked(pinned[0]);
-		} else {
-			unlock_page(pinned[0]);
-		}
-	}
-	if ((pos + iov_iter_count(&i)) & (PAGE_CACHE_SIZE - 1)) {
-		pinned[1] = grab_cache_page(inode->i_mapping, last_index);
-		if (!PageUptodate(pinned[1])) {
-			ret = btrfs_readpage(NULL, pinned[1]);
-			BUG_ON(ret);
-			wait_on_page_locked(pinned[1]);
-		} else {
-			unlock_page(pinned[1]);
-		}
-	}
-
 	while (iov_iter_count(&i) > 0) {
 		size_t offset = pos & (PAGE_CACHE_SIZE - 1);
 		size_t write_bytes = min(iov_iter_count(&i),
@@ -1024,8 +1039,12 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
 
 		copied = btrfs_copy_from_user(pos, num_pages,
 					   write_bytes, pages, &i);
-		dirty_pages = (copied + offset + PAGE_CACHE_SIZE - 1) >>
-				PAGE_CACHE_SHIFT;
+		if (copied == 0)
+			dirty_pages = 0;
+		else
+			dirty_pages = (copied + offset +
+				       PAGE_CACHE_SIZE - 1) >>
+				       PAGE_CACHE_SHIFT;
 
 		if (num_pages > dirty_pages) {
 			if (copied > 0)
@@ -1069,10 +1088,6 @@ out:
 		err = ret;
 
 	kfree(pages);
-	if (pinned[0])
-		page_cache_release(pinned[0]);
-	if (pinned[1])
-		page_cache_release(pinned[1]);
 	*ppos = pos;
 
 	/*

RE: [PATCH] btrfs file write debugging patch

[Zhong, Xin]

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Re: [PATCH] btrfs file write debugging patch

[Johannes Hirte]

On Monday 28 February 2011 02:46:05 Chris Mason wrote:
> Excerpts from Mitch Harder's message of 2011-02-25 13:43:37 -0500:
> > Some clarification on my previous message...
> > 
> > After looking at my ftrace log more closely, I can see where Btrfs is
> > trying to release the allocated pages.  However, the calculation for
> > the number of dirty_pages is equal to 1 when "copied == 0".
> > 
> > So I'm seeing at least two problems:
> > (1)  It keeps looping when "copied == 0".
> > (2)  One dirty page is not being released on every loop even though
> > "copied == 0" (at least this problem keeps it from being an infinite
> > loop by eventually exhausting reserveable space on the disk).
> 
> Hi everyone,
> 
> There are actually tow bugs here.  First the one that Mitch hit, and a
> second one that still results in bad file_write results with my
> debugging hunks (the first two hunks below) in place.
> 
> My patch fixes Mitch's bug by checking for copied == 0 after
> btrfs_copy_from_user and going the correct delalloc accounting.  This
> one looks solved, but you'll notice the patch is bigger.
> 
> First, I add some random failures to btrfs_copy_from_user() by failing
> everyone once and a while.  This was much more reliable than trying to
> use memory pressure than making copy_from_user fail.
> 
> If copy_from_user fails and we partially update a page, we end up with a
> page that may go away due to memory pressure.  But, btrfs_file_write
> assumes that only the first and last page may have good data that needs
> to be read off the disk.
> 
> This patch ditches that code and puts it into prepare_pages instead.
> But I'm still having some errors during long stress.sh runs.  Ideas are
> more than welcome, hopefully some other timezones will kick in ideas
> while I sleep.

At least it doesn't fix the emerge-problem for me. The behavior is now the same 
as with 2.6.38-rc3. It needs a 'emerge --oneshot dev-libs/libgcrypt' with no 
further interaction to get the emerge-process hang with a svn-process 
consuming 100% CPU. I can cancel the emerge-process with ctrl-c but the 
spawned svn-process stays and it needs a reboot to get rid of it. 

Re: [PATCH] btrfs file write debugging patch

[Chris Mason]

Excerpts from Johannes Hirte's message of 2011-02-28 05:13:59 -0500:
> On Monday 28 February 2011 02:46:05 Chris Mason wrote:
> > Excerpts from Mitch Harder's message of 2011-02-25 13:43:37 -0500:
> > > Some clarification on my previous message...
> > > 
> > > After looking at my ftrace log more closely, I can see where Btrfs is
> > > trying to release the allocated pages.  However, the calculation for
> > > the number of dirty_pages is equal to 1 when "copied == 0".
> > > 
> > > So I'm seeing at least two problems:
> > > (1)  It keeps looping when "copied == 0".
> > > (2)  One dirty page is not being released on every loop even though
> > > "copied == 0" (at least this problem keeps it from being an infinite
> > > loop by eventually exhausting reserveable space on the disk).
> > 
> > Hi everyone,
> > 
> > There are actually tow bugs here.  First the one that Mitch hit, and a
> > second one that still results in bad file_write results with my
> > debugging hunks (the first two hunks below) in place.
> > 
> > My patch fixes Mitch's bug by checking for copied == 0 after
> > btrfs_copy_from_user and going the correct delalloc accounting.  This
> > one looks solved, but you'll notice the patch is bigger.
> > 
> > First, I add some random failures to btrfs_copy_from_user() by failing
> > everyone once and a while.  This was much more reliable than trying to
> > use memory pressure than making copy_from_user fail.
> > 
> > If copy_from_user fails and we partially update a page, we end up with a
> > page that may go away due to memory pressure.  But, btrfs_file_write
> > assumes that only the first and last page may have good data that needs
> > to be read off the disk.
> > 
> > This patch ditches that code and puts it into prepare_pages instead.
> > But I'm still having some errors during long stress.sh runs.  Ideas are
> > more than welcome, hopefully some other timezones will kick in ideas
> > while I sleep.
> 
> At least it doesn't fix the emerge-problem for me. The behavior is now the same 
> as with 2.6.38-rc3. It needs a 'emerge --oneshot dev-libs/libgcrypt' with no 
> further interaction to get the emerge-process hang with a svn-process 
> consuming 100% CPU. I can cancel the emerge-process with ctrl-c but the 
> spawned svn-process stays and it needs a reboot to get rid of it. 

I think your problem really is more enospc related.  Still working on
that as well.  But please don't try the patch without removing the
debugging hunk at the top (anything that mentions jiffies).

-chris

RE: [PATCH] btrfs file write debugging patch

[Chris Mason]

Excerpts from Zhong, Xin's message of 2011-02-28 03:56:40 -0500:
> One possible issue I can see is in the random failure case #2 that co=
py_from_user only process half of the data.=20
>=20
> For example, if it write a 4k aligned page and copy_from_user only wr=
ite 2k. Then it will not call btrfs_delalloc_release_space since num_pa=
ges and dirty_pages are both 1.=20
> In the next round, it write another 2k and btrfs_delalloc_reserve_spa=
ce is called twice for the same page.=20
>=20
> Is it a problem? Thanks!

It should be the correct answer.  The result of the short copy_from_use=
r
should be exactly the same as two write calls where one does 2K and the
other does another 2K.

Either way, it shouldn't result in incorrect bytes in the file, which i=
s
still happening for me with the debugging hunks in place.

-chris

>=20
> -----Original Message-----
> From: Chris Mason [mailto:chris.mason@oracle.com]=20
> Sent: Monday, February 28, 2011 9:46 AM
> To: Mitch Harder
> Cc: Maria Wikstr=C3=B6m; Zhong, Xin; Johannes Hirte; linux-btrfs@vger=
=2Ekernel.org
> Subject: [PATCH] btrfs file write debugging patch
>=20
> Excerpts from Mitch Harder's message of 2011-02-25 13:43:37 -0500:
> > Some clarification on my previous message...
> >=20
> > After looking at my ftrace log more closely, I can see where Btrfs =
is
> > trying to release the allocated pages.  However, the calculation fo=
r
> > the number of dirty_pages is equal to 1 when "copied =3D=3D 0".
> >=20
> > So I'm seeing at least two problems:
> > (1)  It keeps looping when "copied =3D=3D 0".
> > (2)  One dirty page is not being released on every loop even though
> > "copied =3D=3D 0" (at least this problem keeps it from being an inf=
inite
> > loop by eventually exhausting reserveable space on the disk).
>=20
> Hi everyone,
>=20
> There are actually tow bugs here.  First the one that Mitch hit, and =
a
> second one that still results in bad file_write results with my
> debugging hunks (the first two hunks below) in place.
>=20
> My patch fixes Mitch's bug by checking for copied =3D=3D 0 after
> btrfs_copy_from_user and going the correct delalloc accounting.  This
> one looks solved, but you'll notice the patch is bigger.
>=20
> First, I add some random failures to btrfs_copy_from_user() by failin=
g
> everyone once and a while.  This was much more reliable than trying t=
o
> use memory pressure than making copy_from_user fail.
>=20
> If copy_from_user fails and we partially update a page, we end up wit=
h a
> page that may go away due to memory pressure.  But, btrfs_file_write
> assumes that only the first and last page may have good data that nee=
ds
> to be read off the disk.
>=20
> This patch ditches that code and puts it into prepare_pages instead.
> But I'm still having some errors during long stress.sh runs.  Ideas a=
re
> more than welcome, hopefully some other timezones will kick in ideas
> while I sleep.
>=20
> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> index 7084140..89a6a26 100644
> --- a/fs/btrfs/file.c
> +++ b/fs/btrfs/file.c
> @@ -54,6 +54,13 @@ static noinline int btrfs_copy_from_user(loff_t po=
s, int num_pages,
>      int offset =3D pos & (PAGE_CACHE_SIZE - 1);
>      int total_copied =3D 0;
> =20
> +    if ((jiffies % 10) =3D=3D 0)
> +        return 0;
> +
> +    if ((jiffies % 25) =3D=3D 0) {
> +        write_bytes /=3D 2;
> +    }
> +
>      while (write_bytes > 0) {
>          size_t count =3D min_t(size_t,
>                       PAGE_CACHE_SIZE - offset, write_bytes);
> @@ -763,6 +770,26 @@ out:
>  }
> =20
>  /*
> + * on error we return an unlocked page and the error value
> + * on success we return a locked page and 0
> + */
> +static int prepare_uptodate_page(struct page *page, u64 pos)
> +{
> +    int ret =3D 0;
> +    if ((pos & (PAGE_CACHE_SIZE - 1)) && !PageUptodate(page)) {
> +        ret =3D btrfs_readpage(NULL, page);
> +        if (ret)
> +            return ret;
> +        lock_page(page);
> +        if (!PageUptodate(page)) {
> +            unlock_page(page);
> +            return -EIO;
> +        }
> +    }
> +    return 0;
> +}
> +
> +/*
>   * this gets pages into the page cache and locks them down, it also =
properly
>   * waits for data=3Dordered extents to finish before allowing the pa=
ges to be
>   * modified.
> @@ -777,6 +804,7 @@ static noinline int prepare_pages(struct btrfs_ro=
ot *root, struct file *file,
>      unsigned long index =3D pos >> PAGE_CACHE_SHIFT;
>      struct inode *inode =3D fdentry(file)->d_inode;
>      int err =3D 0;
> +    int faili =3D 0;
>      u64 start_pos;
>      u64 last_pos;
> =20
> @@ -794,15 +822,24 @@ again:
>      for (i =3D 0; i < num_pages; i++) {
>          pages[i] =3D grab_cache_page(inode->i_mapping, index + i);
>          if (!pages[i]) {
> -            int c;
> -            for (c =3D i - 1; c >=3D 0; c--) {
> -                unlock_page(pages[c]);
> -                page_cache_release(pages[c]);
> -            }
> -            return -ENOMEM;
> +            faili =3D i - 1;
> +            err =3D -ENOMEM;
> +            goto fail;
> +        }
> +
> +        if (i =3D=3D 0)
> +            err =3D prepare_uptodate_page(pages[i], pos);
> +        else if (i =3D=3D num_pages - 1)
> +            err =3D prepare_uptodate_page(pages[i],
> +                            pos + write_bytes);
> +        if (err) {
> +            page_cache_release(pages[i]);
> +            faili =3D i - 1;
> +            goto fail;
>          }
>          wait_on_page_writeback(pages[i]);
>      }
> +    err =3D 0;
>      if (start_pos < inode->i_size) {
>          struct btrfs_ordered_extent *ordered;
>          lock_extent_bits(&BTRFS_I(inode)->io_tree,
> @@ -842,6 +879,14 @@ again:
>          WARN_ON(!PageLocked(pages[i]));
>      }
>      return 0;
> +fail:
> +    while (faili >=3D 0) {
> +        unlock_page(pages[faili]);
> +        page_cache_release(pages[faili]);
> +        faili--;
> +    }
> +    return err;
> +
>  }
> =20
>  static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
> @@ -851,7 +896,6 @@ static ssize_t btrfs_file_aio_write(struct kiocb =
*iocb,
>      struct file *file =3D iocb->ki_filp;
>      struct inode *inode =3D fdentry(file)->d_inode;
>      struct btrfs_root *root =3D BTRFS_I(inode)->root;
> -    struct page *pinned[2];
>      struct page **pages =3D NULL;
>      struct iov_iter i;
>      loff_t *ppos =3D &iocb->ki_pos;
> @@ -872,9 +916,6 @@ static ssize_t btrfs_file_aio_write(struct kiocb =
*iocb,
>      will_write =3D ((file->f_flags & O_DSYNC) || IS_SYNC(inode) ||
>                (file->f_flags & O_DIRECT));
> =20
> -    pinned[0] =3D NULL;
> -    pinned[1] =3D NULL;
> -
>      start_pos =3D pos;
> =20
>      vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);
> @@ -962,32 +1003,6 @@ static ssize_t btrfs_file_aio_write(struct kioc=
b *iocb,
>      first_index =3D pos >> PAGE_CACHE_SHIFT;
>      last_index =3D (pos + iov_iter_count(&i)) >> PAGE_CACHE_SHIFT;
> =20
> -    /*
> -     * there are lots of better ways to do this, but this code
> -     * makes sure the first and last page in the file range are
> -     * up to date and ready for cow
> -     */
> -    if ((pos & (PAGE_CACHE_SIZE - 1))) {
> -        pinned[0] =3D grab_cache_page(inode->i_mapping, first_index)=
;
> -        if (!PageUptodate(pinned[0])) {
> -            ret =3D btrfs_readpage(NULL, pinned[0]);
> -            BUG_ON(ret);
> -            wait_on_page_locked(pinned[0]);
> -        } else {
> -            unlock_page(pinned[0]);
> -        }
> -    }
> -    if ((pos + iov_iter_count(&i)) & (PAGE_CACHE_SIZE - 1)) {
> -        pinned[1] =3D grab_cache_page(inode->i_mapping, last_index);
> -        if (!PageUptodate(pinned[1])) {
> -            ret =3D btrfs_readpage(NULL, pinned[1]);
> -            BUG_ON(ret);
> -            wait_on_page_locked(pinned[1]);
> -        } else {
> -            unlock_page(pinned[1]);
> -        }
> -    }
> -
>      while (iov_iter_count(&i) > 0) {
>          size_t offset =3D pos & (PAGE_CACHE_SIZE - 1);
>          size_t write_bytes =3D min(iov_iter_count(&i),
> @@ -1024,8 +1039,12 @@ static ssize_t btrfs_file_aio_write(struct kio=
cb *iocb,
> =20
>          copied =3D btrfs_copy_from_user(pos, num_pages,
>                         write_bytes, pages, &i);
> -        dirty_pages =3D (copied + offset + PAGE_CACHE_SIZE - 1) >>
> -                PAGE_CACHE_SHIFT;
> +        if (copied =3D=3D 0)
> +            dirty_pages =3D 0;
> +        else
> +            dirty_pages =3D (copied + offset +
> +                       PAGE_CACHE_SIZE - 1) >>
> +                       PAGE_CACHE_SHIFT;
> =20
>          if (num_pages > dirty_pages) {
>              if (copied > 0)
> @@ -1069,10 +1088,6 @@ out:
>          err =3D ret;
> =20
>      kfree(pages);
> -    if (pinned[0])
> -        page_cache_release(pinned[0]);
> -    if (pinned[1])
> -        page_cache_release(pinned[1]);
>      *ppos =3D pos;
> =20
>      /*
--
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Re: [PATCH] btrfs file write debugging patch

[Josef Bacik]

On Mon, Feb 28, 2011 at 11:13:59AM +0100, Johannes Hirte wrote:
> On Monday 28 February 2011 02:46:05 Chris Mason wrote:
> > Excerpts from Mitch Harder's message of 2011-02-25 13:43:37 -0500:
> > > Some clarification on my previous message...
> > > 
> > > After looking at my ftrace log more closely, I can see where Btrfs is
> > > trying to release the allocated pages.  However, the calculation for
> > > the number of dirty_pages is equal to 1 when "copied == 0".
> > > 
> > > So I'm seeing at least two problems:
> > > (1)  It keeps looping when "copied == 0".
> > > (2)  One dirty page is not being released on every loop even though
> > > "copied == 0" (at least this problem keeps it from being an infinite
> > > loop by eventually exhausting reserveable space on the disk).
> > 
> > Hi everyone,
> > 
> > There are actually tow bugs here.  First the one that Mitch hit, and a
> > second one that still results in bad file_write results with my
> > debugging hunks (the first two hunks below) in place.
> > 
> > My patch fixes Mitch's bug by checking for copied == 0 after
> > btrfs_copy_from_user and going the correct delalloc accounting.  This
> > one looks solved, but you'll notice the patch is bigger.
> > 
> > First, I add some random failures to btrfs_copy_from_user() by failing
> > everyone once and a while.  This was much more reliable than trying to
> > use memory pressure than making copy_from_user fail.
> > 
> > If copy_from_user fails and we partially update a page, we end up with a
> > page that may go away due to memory pressure.  But, btrfs_file_write
> > assumes that only the first and last page may have good data that needs
> > to be read off the disk.
> > 
> > This patch ditches that code and puts it into prepare_pages instead.
> > But I'm still having some errors during long stress.sh runs.  Ideas are
> > more than welcome, hopefully some other timezones will kick in ideas
> > while I sleep.
> 
> At least it doesn't fix the emerge-problem for me. The behavior is now the same 
> as with 2.6.38-rc3. It needs a 'emerge --oneshot dev-libs/libgcrypt' with no 
> further interaction to get the emerge-process hang with a svn-process 
> consuming 100% CPU. I can cancel the emerge-process with ctrl-c but the 
> spawned svn-process stays and it needs a reboot to get rid of it. 

Can you cat /proc/$pid/wchan a few times so we can get an idea of where it's
looping?  Thanks,

Josef

Re: [PATCH] btrfs file write debugging patch

[Maria Wikström]

m=C3=A5n 2011-02-28 klockan 11:10 -0500 skrev Josef Bacik:
> On Mon, Feb 28, 2011 at 11:13:59AM +0100, Johannes Hirte wrote:
> > On Monday 28 February 2011 02:46:05 Chris Mason wrote:
> > > Excerpts from Mitch Harder's message of 2011-02-25 13:43:37 -0500=
:
> > > > Some clarification on my previous message...
> > > >=20
> > > > After looking at my ftrace log more closely, I can see where Bt=
rfs is
> > > > trying to release the allocated pages.  However, the calculatio=
n for
> > > > the number of dirty_pages is equal to 1 when "copied =3D=3D 0".
> > > >=20
> > > > So I'm seeing at least two problems:
> > > > (1)  It keeps looping when "copied =3D=3D 0".
> > > > (2)  One dirty page is not being released on every loop even th=
ough
> > > > "copied =3D=3D 0" (at least this problem keeps it from being an=
 infinite
> > > > loop by eventually exhausting reserveable space on the disk).
> > >=20
> > > Hi everyone,
> > >=20
> > > There are actually tow bugs here.  First the one that Mitch hit, =
and a
> > > second one that still results in bad file_write results with my
> > > debugging hunks (the first two hunks below) in place.
> > >=20
> > > My patch fixes Mitch's bug by checking for copied =3D=3D 0 after
> > > btrfs_copy_from_user and going the correct delalloc accounting.  =
This
> > > one looks solved, but you'll notice the patch is bigger.
> > >=20
> > > First, I add some random failures to btrfs_copy_from_user() by fa=
iling
> > > everyone once and a while.  This was much more reliable than tryi=
ng to
> > > use memory pressure than making copy_from_user fail.
> > >=20
> > > If copy_from_user fails and we partially update a page, we end up=
 with a
> > > page that may go away due to memory pressure.  But, btrfs_file_wr=
ite
> > > assumes that only the first and last page may have good data that=
 needs
> > > to be read off the disk.
> > >=20
> > > This patch ditches that code and puts it into prepare_pages inste=
ad.
> > > But I'm still having some errors during long stress.sh runs.  Ide=
as are
> > > more than welcome, hopefully some other timezones will kick in id=
eas
> > > while I sleep.
> >=20
> > At least it doesn't fix the emerge-problem for me. The behavior is =
now the same=20
> > as with 2.6.38-rc3. It needs a 'emerge --oneshot dev-libs/libgcrypt=
' with no=20
> > further interaction to get the emerge-process hang with a svn-proce=
ss=20
> > consuming 100% CPU. I can cancel the emerge-process with ctrl-c but=
 the=20
> > spawned svn-process stays and it needs a reboot to get rid of it.=20
>=20
> Can you cat /proc/$pid/wchan a few times so we can get an idea of whe=
re it's
> looping?  Thanks,
>=20
> Josef

It behaves the same way here with btrfs-unstable.
The output of "cat /proc/$pid/wchan" is 0.=20

// Maria

> --
> To unsubscribe from this list: send the line "unsubscribe linux-btrfs=
" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>=20


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Re: [PATCH] btrfs file write debugging patch

[Mitch Harder]

[-- Attachment #1: Type: text/plain, Size: 3729 bytes --]

2011/2/28 Maria Wikström <maria@ponstudios.se>:
> mån 2011-02-28 klockan 11:10 -0500 skrev Josef Bacik:
>> On Mon, Feb 28, 2011 at 11:13:59AM +0100, Johannes Hirte wrote:
>> > On Monday 28 February 2011 02:46:05 Chris Mason wrote:
>> > > Excerpts from Mitch Harder's message of 2011-02-25 13:43:37 -0500:
>> > > > Some clarification on my previous message...
>> > > >
>> > > > After looking at my ftrace log more closely, I can see where Btrfs is
>> > > > trying to release the allocated pages.  However, the calculation for
>> > > > the number of dirty_pages is equal to 1 when "copied == 0".
>> > > >
>> > > > So I'm seeing at least two problems:
>> > > > (1)  It keeps looping when "copied == 0".
>> > > > (2)  One dirty page is not being released on every loop even though
>> > > > "copied == 0" (at least this problem keeps it from being an infinite
>> > > > loop by eventually exhausting reserveable space on the disk).
>> > >
>> > > Hi everyone,
>> > >
>> > > There are actually tow bugs here.  First the one that Mitch hit, and a
>> > > second one that still results in bad file_write results with my
>> > > debugging hunks (the first two hunks below) in place.
>> > >
>> > > My patch fixes Mitch's bug by checking for copied == 0 after
>> > > btrfs_copy_from_user and going the correct delalloc accounting.  This
>> > > one looks solved, but you'll notice the patch is bigger.
>> > >
>> > > First, I add some random failures to btrfs_copy_from_user() by failing
>> > > everyone once and a while.  This was much more reliable than trying to
>> > > use memory pressure than making copy_from_user fail.
>> > >
>> > > If copy_from_user fails and we partially update a page, we end up with a
>> > > page that may go away due to memory pressure.  But, btrfs_file_write
>> > > assumes that only the first and last page may have good data that needs
>> > > to be read off the disk.
>> > >
>> > > This patch ditches that code and puts it into prepare_pages instead.
>> > > But I'm still having some errors during long stress.sh runs.  Ideas are
>> > > more than welcome, hopefully some other timezones will kick in ideas
>> > > while I sleep.
>> >
>> > At least it doesn't fix the emerge-problem for me. The behavior is now the same
>> > as with 2.6.38-rc3. It needs a 'emerge --oneshot dev-libs/libgcrypt' with no
>> > further interaction to get the emerge-process hang with a svn-process
>> > consuming 100% CPU. I can cancel the emerge-process with ctrl-c but the
>> > spawned svn-process stays and it needs a reboot to get rid of it.
>>
>> Can you cat /proc/$pid/wchan a few times so we can get an idea of where it's
>> looping?  Thanks,
>>
>> Josef
>
> It behaves the same way here with btrfs-unstable.
> The output of "cat /proc/$pid/wchan" is 0.
>
> // Maria
>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
>
>
>

I've applied the patch at the head of this thread (with the jiffies
debugging commented out) and I'm attaching a ftrace using the
function_graph tracer when I'm stuck in the loop.  I've just snipped
out a couple of the loops (the full trace file is quite large, and
mostly repititious).

I'm going to try to modify file.c with some trace_printk debugging to
show the values of several of the relevant variables at various
stages.

I'm going to try to exit the loop after 256 tries with an EFAULT so I
can stop the tracing at that point and capture a trace of the entry
into the problem (the ftrace ring buffer fills up too fast for me to
capture the entry point).

[-- Attachment #2: ftrace-btrfs-file-write-debugging.gz --]
[-- Type: application/x-gzip, Size: 2590 bytes --]

Re: [PATCH] btrfs file write debugging patch

[Mitch Harder]

2011/2/28 Mitch Harder <mitch.harder@sabayonlinux.org>:
> 2011/2/28 Maria Wikstr=F6m <maria@ponstudios.se>:
>> m=E5n 2011-02-28 klockan 11:10 -0500 skrev Josef Bacik:
>>> On Mon, Feb 28, 2011 at 11:13:59AM +0100, Johannes Hirte wrote:
>>> > On Monday 28 February 2011 02:46:05 Chris Mason wrote:
>>> > > Excerpts from Mitch Harder's message of 2011-02-25 13:43:37 -05=
00:
>>> > > > Some clarification on my previous message...
>>> > > >
>>> > > > After looking at my ftrace log more closely, I can see where =
Btrfs is
>>> > > > trying to release the allocated pages. =A0However, the calcul=
ation for
>>> > > > the number of dirty_pages is equal to 1 when "copied =3D=3D 0=
".
>>> > > >
>>> > > > So I'm seeing at least two problems:
>>> > > > (1) =A0It keeps looping when "copied =3D=3D 0".
>>> > > > (2) =A0One dirty page is not being released on every loop eve=
n though
>>> > > > "copied =3D=3D 0" (at least this problem keeps it from being =
an infinite
>>> > > > loop by eventually exhausting reserveable space on the disk).
>>> > >
>>> > > Hi everyone,
>>> > >
>>> > > There are actually tow bugs here. =A0First the one that Mitch h=
it, and a
>>> > > second one that still results in bad file_write results with my
>>> > > debugging hunks (the first two hunks below) in place.
>>> > >
>>> > > My patch fixes Mitch's bug by checking for copied =3D=3D 0 afte=
r
>>> > > btrfs_copy_from_user and going the correct delalloc accounting.=
 =A0This
>>> > > one looks solved, but you'll notice the patch is bigger.
>>> > >
>>> > > First, I add some random failures to btrfs_copy_from_user() by =
failing
>>> > > everyone once and a while. =A0This was much more reliable than =
trying to
>>> > > use memory pressure than making copy_from_user fail.
>>> > >
>>> > > If copy_from_user fails and we partially update a page, we end =
up with a
>>> > > page that may go away due to memory pressure. =A0But, btrfs_fil=
e_write
>>> > > assumes that only the first and last page may have good data th=
at needs
>>> > > to be read off the disk.
>>> > >
>>> > > This patch ditches that code and puts it into prepare_pages ins=
tead.
>>> > > But I'm still having some errors during long stress.sh runs. =A0=
Ideas are
>>> > > more than welcome, hopefully some other timezones will kick in =
ideas
>>> > > while I sleep.
>>> >
>>> > At least it doesn't fix the emerge-problem for me. The behavior i=
s now the same
>>> > as with 2.6.38-rc3. It needs a 'emerge --oneshot dev-libs/libgcry=
pt' with no
>>> > further interaction to get the emerge-process hang with a svn-pro=
cess
>>> > consuming 100% CPU. I can cancel the emerge-process with ctrl-c b=
ut the
>>> > spawned svn-process stays and it needs a reboot to get rid of it.
>>>
>>> Can you cat /proc/$pid/wchan a few times so we can get an idea of w=
here it's
>>> looping? =A0Thanks,
>>>
>>> Josef
>>
>> It behaves the same way here with btrfs-unstable.
>> The output of "cat /proc/$pid/wchan" is 0.
>>
>> // Maria
>>
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-btr=
fs" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at =A0http://vger.kernel.org/majordomo-info.htm=
l
>>>
>>
>>
>>
>
> I've applied the patch at the head of this thread (with the jiffies
> debugging commented out) and I'm attaching a ftrace using the
> function_graph tracer when I'm stuck in the loop. =A0I've just snippe=
d
> out a couple of the loops (the full trace file is quite large, and
> mostly repititious).
>
> I'm going to try to modify file.c with some trace_printk debugging to
> show the values of several of the relevant variables at various
> stages.
>
> I'm going to try to exit the loop after 256 tries with an EFAULT so I
> can stop the tracing at that point and capture a trace of the entry
> into the problem (the ftrace ring buffer fills up too fast for me to
> capture the entry point).
>

As promised, I'm put together a modified file.c with many trace_printk
debugging statements to augment the ftrace.

The trace is ~128K compressed (about 31,600 lines or 2.6MB
uncompressed), so I'm putting it up on my local server instead of
attaching.  Let me know if it would be more appropriate to send to the
list as an attachment.

http://dontpanic.dyndns.org/ftrace-btrfs-file-write-debug-v2.gz

I preface all my trace_printk comments with "TPK:" to make skipping
through the trace easier.

The trace contains the trace of about 3 or 4 successful passes through
the btrfs_file_aio_write() function to show what a successful trace
looks like.

The pass through the btrfs_file_aio_write() that breaks begins on line =
1088.

I let it loop through the while (iov_iter_count(&i) > 0) {} loop for
256 times when copied=3D=3D0 (otherwise it would loop infinitely).  The=
n
exit out and stop the trace.

=46or reference, here's a diff file for the debugging statements I've
added to file.c:

Let me know if you would like me to re-run this trial with different
debugging lines.

 fs/btrfs/file.c /usr/src/linux/fs/btrfs/file.c
--- fs/btrfs/file.c	2011-02-28 10:13:45.000000000 -0600
+++ /usr/src/linux/fs/btrfs/file.c	2011-02-28 13:07:11.000000000 -0600
@@ -53,12 +53,14 @@
 	int offset =3D pos & (PAGE_CACHE_SIZE - 1);
 	int total_copied =3D 0;

+	/***************************
 	if ((jiffies % 10) =3D=3D 0)
 		return 0;

 	if ((jiffies % 25) =3D=3D 0) {
 		write_bytes /=3D 2;
 	}
+	**************************/

 	while (write_bytes > 0) {
 		size_t count =3D min_t(size_t,
@@ -82,10 +84,13 @@

 		/* Return to btrfs_file_aio_write to fault page */
 		if (unlikely(copied =3D=3D 0)) {
+			trace_printk("TPK: unlikely copied =3D=3D 0 in btrfs_copy_from_user
(total_copied=3D%i)\n",
+				     total_copied);
 			break;
 		}

 		if (unlikely(copied < PAGE_CACHE_SIZE - offset)) {
+			trace_printk("TPK: unlikely copied < PAGE_CACHE_SIZE - offset in
btrfs_copy_from_user\n");
 			offset +=3D copied;
 		} else {
 			pg++;
@@ -910,8 +915,13 @@
 	int will_write;
 	int buffered =3D 0;
 	int copied =3D 0;
+	int copied_problem =3D 0;
+	int copied_loop_count =3D 0;
+	int stop_ftrace =3D 0;
 	int dirty_pages =3D 0;

+	trace_printk("TPK: Entering btrfs_file_aio_write()\n");
+
 	will_write =3D ((file->f_flags & O_DSYNC) || IS_SYNC(inode) ||
 		      (file->f_flags & O_DIRECT));

@@ -953,6 +963,7 @@
 	BTRFS_I(inode)->sequence++;

 	if (unlikely(file->f_flags & O_DIRECT)) {
+		trace_printk("TPK: transferred to unlikely(file->f_flags \& O_DIRECT=
)\n");
 		num_written =3D generic_file_direct_write(iocb, iov, &nr_segs,
 							pos, ppos, count,
 							ocount);
@@ -984,6 +995,8 @@
 		 */
 		buffered =3D 1;
 		pos +=3D num_written;
+		trace_printk("TPK: end unlikely(file->f_flags \& O_DIRECT) with
num_written=3D%i\n",
+			     num_written);
 	}

 	iov_iter_init(&i, iov, nr_segs, count, num_written);
@@ -1003,6 +1016,8 @@
 	last_index =3D (pos + iov_iter_count(&i)) >> PAGE_CACHE_SHIFT;

 	while (iov_iter_count(&i) > 0) {
+		trace_printk("TPK: start section while (iov_iter_count() > 0)\n");
+
 		size_t offset =3D pos & (PAGE_CACHE_SIZE - 1);
 		size_t write_bytes =3D min(iov_iter_count(&i),
 					 nrptrs * (size_t)PAGE_CACHE_SIZE -
@@ -1010,6 +1025,9 @@
 		size_t num_pages =3D (write_bytes + offset +
 				    PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;

+		trace_printk("TPK: iov_iter_count()=3D%i || nr_segs=3D%lu || nrptrs=3D=
%i
|| offset=3D%lu || write_bytes=3D%lu || num_pages=3D%lu\n",
+						iov_iter_count(&i), nr_segs, nrptrs, offset, write_bytes, num_pa=
ges);
+
 		WARN_ON(num_pages > nrptrs);
 		memset(pages, 0, sizeof(struct page *) * nrptrs);

@@ -1022,6 +1040,19 @@
 			goto out;
 		}

+		if (unlikely(copied_problem)) {
+			copied_loop_count++;
+			trace_printk("TPK: copied problem(%i)\n",
+				     copied_loop_count);
+			/* Give up if we've already tried 256 times */
+			if (copied_loop_count > 256) {
+				ret =3D -EFAULT;
+				stop_ftrace =3D 1;
+				trace_printk("TPK: copied loop count exceeded, returning EFAULT...=
=2E\n");
+				goto out;
+			}
+		}
+
 		ret =3D btrfs_delalloc_reserve_space(inode,
 					num_pages << PAGE_CACHE_SHIFT);
 		if (ret)
@@ -1045,6 +1076,10 @@
 				       PAGE_CACHE_SIZE - 1) >>
 				       PAGE_CACHE_SHIFT;

+		if (copied =3D=3D 0) {
+			copied_problem =3D 1;
+		}
+
 		if (num_pages > dirty_pages) {
 			if (copied > 0)
 				atomic_inc(
@@ -1080,11 +1115,19 @@
 		num_written +=3D copied;

 		cond_resched();
+		trace_printk("TPK: end section while (iov_iter_count() > 0)\n");
+		trace_printk(" copied=3D%i || dirty_pages=3D%i || num_written=3D%i |=
|
ending iov_iter_count=3D%i\n",
+						copied, dirty_pages, num_written, iov_iter_count(&i) );
 	}
 out:
+	trace_printk("TPK: Reached: out:\n");
+
 	mutex_unlock(&inode->i_mutex);
-	if (ret)
+	if (ret) {
 		err =3D ret;
+		trace_printk("TPK: ret,err had value %i when out: was reached
(num_written: %i)\n",
+			     ret, num_written);
+	}

 	kfree(pages);
 	*ppos =3D pos;
@@ -1140,6 +1183,19 @@
 	}
 done:
 	current->backing_dev_info =3D NULL;
+	if (ret) {
+		trace_printk("TPK: btrfs_file_aio_write exiting with non-zero ret
value (%i)\n", ret);
+		trace_printk("TPK: Returning num_written (%i) ? num_written (%i) :
err (%i) =3D %i\n",
+				num_written, num_written, err, num_written ? num_written : err);
+	} else {
+		trace_printk("TPK: btrfs_file_aio_write exiting normally with (%i)",
+			     num_written ? num_written : err);
+	}
+=09
+	if (unlikely(stop_ftrace)) {
+		tracing_off();
+	}
+
 	return num_written ? num_written : err;
 }
--
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Re: [PATCH] btrfs file write debugging patch

[Mitch Harder]

2011/2/28 Mitch Harder <mitch.harder@sabayonlinux.org>:
> 2011/2/28 Mitch Harder <mitch.harder@sabayonlinux.org>:
>> 2011/2/28 Maria Wikstr=F6m <maria@ponstudios.se>:
>>> m=E5n 2011-02-28 klockan 11:10 -0500 skrev Josef Bacik:
>>>> On Mon, Feb 28, 2011 at 11:13:59AM +0100, Johannes Hirte wrote:
>>>> > On Monday 28 February 2011 02:46:05 Chris Mason wrote:
>>>> > > Excerpts from Mitch Harder's message of 2011-02-25 13:43:37 -0=
500:
>>>> > > > Some clarification on my previous message...
>>>> > > >
>>>> > > > After looking at my ftrace log more closely, I can see where=
 Btrfs is
>>>> > > > trying to release the allocated pages. =A0However, the calcu=
lation for
>>>> > > > the number of dirty_pages is equal to 1 when "copied =3D=3D =
0".
>>>> > > >
>>>> > > > So I'm seeing at least two problems:
>>>> > > > (1) =A0It keeps looping when "copied =3D=3D 0".
>>>> > > > (2) =A0One dirty page is not being released on every loop ev=
en though
>>>> > > > "copied =3D=3D 0" (at least this problem keeps it from being=
 an infinite
>>>> > > > loop by eventually exhausting reserveable space on the disk)=
=2E
>>>> > >
>>>> > > Hi everyone,
>>>> > >
>>>> > > There are actually tow bugs here. =A0First the one that Mitch =
hit, and a
>>>> > > second one that still results in bad file_write results with m=
y
>>>> > > debugging hunks (the first two hunks below) in place.
>>>> > >
>>>> > > My patch fixes Mitch's bug by checking for copied =3D=3D 0 aft=
er
>>>> > > btrfs_copy_from_user and going the correct delalloc accounting=
=2E =A0This
>>>> > > one looks solved, but you'll notice the patch is bigger.
>>>> > >
>>>> > > First, I add some random failures to btrfs_copy_from_user() by=
 failing
>>>> > > everyone once and a while. =A0This was much more reliable than=
 trying to
>>>> > > use memory pressure than making copy_from_user fail.
>>>> > >
>>>> > > If copy_from_user fails and we partially update a page, we end=
 up with a
>>>> > > page that may go away due to memory pressure. =A0But, btrfs_fi=
le_write
>>>> > > assumes that only the first and last page may have good data t=
hat needs
>>>> > > to be read off the disk.
>>>> > >
>>>> > > This patch ditches that code and puts it into prepare_pages in=
stead.
>>>> > > But I'm still having some errors during long stress.sh runs. =A0=
Ideas are
>>>> > > more than welcome, hopefully some other timezones will kick in=
 ideas
>>>> > > while I sleep.
>>>> >
>>>> > At least it doesn't fix the emerge-problem for me. The behavior =
is now the same
>>>> > as with 2.6.38-rc3. It needs a 'emerge --oneshot dev-libs/libgcr=
ypt' with no
>>>> > further interaction to get the emerge-process hang with a svn-pr=
ocess
>>>> > consuming 100% CPU. I can cancel the emerge-process with ctrl-c =
but the
>>>> > spawned svn-process stays and it needs a reboot to get rid of it=
=2E
>>>>
>>>> Can you cat /proc/$pid/wchan a few times so we can get an idea of =
where it's
>>>> looping? =A0Thanks,
>>>>
>>>> Josef
>>>
>>> It behaves the same way here with btrfs-unstable.
>>> The output of "cat /proc/$pid/wchan" is 0.
>>>
>>> // Maria
>>>
>>>> --
>>>> To unsubscribe from this list: send the line "unsubscribe linux-bt=
rfs" in
>>>> the body of a message to majordomo@vger.kernel.org
>>>> More majordomo info at =A0http://vger.kernel.org/majordomo-info.ht=
ml
>>>>
>>>
>>>
>>>
>>
>> I've applied the patch at the head of this thread (with the jiffies
>> debugging commented out) and I'm attaching a ftrace using the
>> function_graph tracer when I'm stuck in the loop. =A0I've just snipp=
ed
>> out a couple of the loops (the full trace file is quite large, and
>> mostly repititious).
>>
>> I'm going to try to modify file.c with some trace_printk debugging t=
o
>> show the values of several of the relevant variables at various
>> stages.
>>
>> I'm going to try to exit the loop after 256 tries with an EFAULT so =
I
>> can stop the tracing at that point and capture a trace of the entry
>> into the problem (the ftrace ring buffer fills up too fast for me to
>> capture the entry point).
>>
>
> As promised, I'm put together a modified file.c with many trace_print=
k
> debugging statements to augment the ftrace.
>
> The trace is ~128K compressed (about 31,600 lines or 2.6MB
> uncompressed), so I'm putting it up on my local server instead of
> attaching. =A0Let me know if it would be more appropriate to send to =
the
> list as an attachment.
>
> http://dontpanic.dyndns.org/ftrace-btrfs-file-write-debug-v2.gz
>
> I preface all my trace_printk comments with "TPK:" to make skipping
> through the trace easier.
>
> The trace contains the trace of about 3 or 4 successful passes throug=
h
> the btrfs_file_aio_write() function to show what a successful trace
> looks like.
>
> The pass through the btrfs_file_aio_write() that breaks begins on lin=
e 1088.
>
> I let it loop through the while (iov_iter_count(&i) > 0) {} loop for
> 256 times when copied=3D=3D0 (otherwise it would loop infinitely). =A0=
Then
> exit out and stop the trace.
>
> For reference, here's a diff file for the debugging statements I've
> added to file.c:
>
> Let me know if you would like me to re-run this trial with different
> debugging lines.
>
> =A0fs/btrfs/file.c /usr/src/linux/fs/btrfs/file.c
> --- fs/btrfs/file.c =A0 =A0 2011-02-28 10:13:45.000000000 -0600
> +++ /usr/src/linux/fs/btrfs/file.c =A0 =A0 =A02011-02-28 13:07:11.000=
000000 -0600
> @@ -53,12 +53,14 @@
> =A0 =A0 =A0 =A0int offset =3D pos & (PAGE_CACHE_SIZE - 1);
> =A0 =A0 =A0 =A0int total_copied =3D 0;
>
> + =A0 =A0 =A0 /***************************
> =A0 =A0 =A0 =A0if ((jiffies % 10) =3D=3D 0)
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0return 0;
>
> =A0 =A0 =A0 =A0if ((jiffies % 25) =3D=3D 0) {
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0write_bytes /=3D 2;
> =A0 =A0 =A0 =A0}
> + =A0 =A0 =A0 **************************/
>
> =A0 =A0 =A0 =A0while (write_bytes > 0) {
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0size_t count =3D min_t(size_t,
> @@ -82,10 +84,13 @@
>
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0/* Return to btrfs_file_aio_write to f=
ault page */
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0if (unlikely(copied =3D=3D 0)) {
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 trace_printk("TPK: unli=
kely copied =3D=3D 0 in btrfs_copy_from_user
> (total_copied=3D%i)\n",
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0total_copied);
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0break;
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0}
>
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0if (unlikely(copied < PAGE_CACHE_SIZE =
- offset)) {
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 trace_printk("TPK: unli=
kely copied < PAGE_CACHE_SIZE - offset in
> btrfs_copy_from_user\n");
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0offset +=3D copied;
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0} else {
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0pg++;
> @@ -910,8 +915,13 @@
> =A0 =A0 =A0 =A0int will_write;
> =A0 =A0 =A0 =A0int buffered =3D 0;
> =A0 =A0 =A0 =A0int copied =3D 0;
> + =A0 =A0 =A0 int copied_problem =3D 0;
> + =A0 =A0 =A0 int copied_loop_count =3D 0;
> + =A0 =A0 =A0 int stop_ftrace =3D 0;
> =A0 =A0 =A0 =A0int dirty_pages =3D 0;
>
> + =A0 =A0 =A0 trace_printk("TPK: Entering btrfs_file_aio_write()\n");
> +
> =A0 =A0 =A0 =A0will_write =3D ((file->f_flags & O_DSYNC) || IS_SYNC(i=
node) ||
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0(file->f_flags & O_DIRECT)=
);
>
> @@ -953,6 +963,7 @@
> =A0 =A0 =A0 =A0BTRFS_I(inode)->sequence++;
>
> =A0 =A0 =A0 =A0if (unlikely(file->f_flags & O_DIRECT)) {
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 trace_printk("TPK: transferred to unlik=
ely(file->f_flags \& O_DIRECT)\n");
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0num_written =3D generic_file_direct_wr=
ite(iocb, iov, &nr_segs,
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0pos, ppos, count,
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0ocount);
> @@ -984,6 +995,8 @@
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 */
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0buffered =3D 1;
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0pos +=3D num_written;
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 trace_printk("TPK: end unlikely(file->f=
_flags \& O_DIRECT) with
> num_written=3D%i\n",
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0num_written)=
;
> =A0 =A0 =A0 =A0}
>
> =A0 =A0 =A0 =A0iov_iter_init(&i, iov, nr_segs, count, num_written);
> @@ -1003,6 +1016,8 @@
> =A0 =A0 =A0 =A0last_index =3D (pos + iov_iter_count(&i)) >> PAGE_CACH=
E_SHIFT;
>
> =A0 =A0 =A0 =A0while (iov_iter_count(&i) > 0) {
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 trace_printk("TPK: start section while =
(iov_iter_count() > 0)\n");
> +
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0size_t offset =3D pos & (PAGE_CACHE_SI=
ZE - 1);
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0size_t write_bytes =3D min(iov_iter_co=
unt(&i),
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0 nrptrs * (size_t)PAGE_CACHE_SIZE -
> @@ -1010,6 +1025,9 @@
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0size_t num_pages =3D (write_bytes + of=
fset +
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
>
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 trace_printk("TPK: iov_iter_count()=3D%=
i || nr_segs=3D%lu || nrptrs=3D%i
> || offset=3D%lu || write_bytes=3D%lu || num_pages=3D%lu\n",
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0 =A0 =A0 =A0 =A0 iov_iter_count(&i), nr_segs, nrptrs, offset, w=
rite_bytes, num_pages);
> +
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0WARN_ON(num_pages > nrptrs);
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0memset(pages, 0, sizeof(struct page *)=
 * nrptrs);
>
> @@ -1022,6 +1040,19 @@
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0goto out;
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0}
>
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (unlikely(copied_problem)) {
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 copied_loop_count++;
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 trace_printk("TPK: copi=
ed problem(%i)\n",
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0copied_loop_count);
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 /* Give up if we've alr=
eady tried 256 times */
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (copied_loop_count >=
 256) {
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ret =3D=
 -EFAULT;
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 stop_ft=
race =3D 1;
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 trace_p=
rintk("TPK: copied loop count exceeded, returning EFAULT....\n");
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 goto ou=
t;
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 }
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 }
> +
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0ret =3D btrfs_delalloc_reserve_space(i=
node,
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0num_pages << PAGE_CACHE_SHIFT);
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0if (ret)
> @@ -1045,6 +1076,10 @@
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 PAGE_CACHE_SIZE - 1) >>
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 PAGE_CACHE_SHIFT;
>
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (copied =3D=3D 0) {
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 copied_problem =3D 1;
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 }
> +
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0if (num_pages > dirty_pages) {
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0if (copied > 0)
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0atomic=
_inc(
> @@ -1080,11 +1115,19 @@
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0num_written +=3D copied;
>
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0cond_resched();
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 trace_printk("TPK: end section while (i=
ov_iter_count() > 0)\n");
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 trace_printk(" copied=3D%i || dirty_pag=
es=3D%i || num_written=3D%i ||
> ending iov_iter_count=3D%i\n",
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0 =A0 =A0 =A0 =A0 copied, dirty_pages, num_written, iov_iter_cou=
nt(&i) );
> =A0 =A0 =A0 =A0}
> =A0out:
> + =A0 =A0 =A0 trace_printk("TPK: Reached: out:\n");
> +
> =A0 =A0 =A0 =A0mutex_unlock(&inode->i_mutex);
> - =A0 =A0 =A0 if (ret)
> + =A0 =A0 =A0 if (ret) {
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0err =3D ret;
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 trace_printk("TPK: ret,err had value %i=
 when out: was reached
> (num_written: %i)\n",
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0ret, num_wri=
tten);
> + =A0 =A0 =A0 }
>
> =A0 =A0 =A0 =A0kfree(pages);
> =A0 =A0 =A0 =A0*ppos =3D pos;
> @@ -1140,6 +1183,19 @@
> =A0 =A0 =A0 =A0}
> =A0done:
> =A0 =A0 =A0 =A0current->backing_dev_info =3D NULL;
> + =A0 =A0 =A0 if (ret) {
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 trace_printk("TPK: btrfs_file_aio_write=
 exiting with non-zero ret
> value (%i)\n", ret);
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 trace_printk("TPK: Returning num_writte=
n (%i) ? num_written (%i) :
> err (%i) =3D %i\n",
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 num_wri=
tten, num_written, err, num_written ? num_written : err);
> + =A0 =A0 =A0 } else {
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 trace_printk("TPK: btrfs_file_aio_write=
 exiting normally with (%i)",
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0num_written =
? num_written : err);
> + =A0 =A0 =A0 }
> +
> + =A0 =A0 =A0 if (unlikely(stop_ftrace)) {
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 tracing_off();
> + =A0 =A0 =A0 }
> +
> =A0 =A0 =A0 =A0return num_written ? num_written : err;
> =A0}
>

I'm developing a hypothesis that something is going wrong when Btrfs
is trying to lock multiple pages.

Page faults are being encountered at the same spot, over and over
(BTW, I ran a memcheck to rule that possibility out).

If I scan through my traces, it looks like most calls to write are
submitted 1 block (4096 bytes) at a time, at the most (also many are <
4096 bytes).  The portion that is causing a problem is trying to write
12288 bytes (3k).  For some reason, the first 24 bytes are written,
and the remainder of the loop is spent on the 12264 that are
remaining.  But page faults are encountered on each loop, and no more
bytes are copied.

I modified file.c to cut back on the scope of the attempted write to
smaller chunks.

The following patch "fixes" my problem, and this build completes
without error.  I'm not submitting this patch as a solution.  It's
clearly papering over a deeper issue.  However, I think it gives
insight into the problem.

I wrote the patch to allow for sequentially smaller blocks if failures
continue.  But the block cleared once I limited the scope to 4096
bytes.  It never needed to try smaller data segments.

As hoped, limiting the scope of the write allowed the 12264 bytes to
be written in the next three subsequent loops after lowering the scope
of the write.

It was interesting to note that cutting the scope to 4096 didn't
guarantee that you were limiting the write to one block. There was
usually some overlap, and 2 dirty block needed to be written.  But I'm
still suspicious that there is a mismatch somewhere when trying to
lock multiple blocks.

Here's the debugging patch I constructed which actually allowed the
build to complete without error.  This was applied (for testing
purposes) on top of the previous debugging patch.  As noted earlier,
it never went lower than a 4096 byte window for write_bytes.

--- file.c.file-write-patch-v1	2011-02-28 13:06:37.000000000 -0600
+++ file.c	2011-02-28 19:23:21.000000000 -0600
@@ -908,6 +908,7 @@
 	ssize_t err =3D 0;
 	size_t count;
 	size_t ocount;
+	size_t write_bytes =3D 0;
 	int ret =3D 0;
 	int nrptrs;
 	unsigned long first_index;
@@ -963,7 +964,7 @@
 	BTRFS_I(inode)->sequence++;

 	if (unlikely(file->f_flags & O_DIRECT)) {
-		trace_printk("TPK: transferred to unlikely(file->f_flags \& O_DIRECT=
)\n");
+		trace_printk("TPK: transferred to unlikely(file->f_flags & O_DIRECT)=
\n");
 		num_written =3D generic_file_direct_write(iocb, iov, &nr_segs,
 							pos, ppos, count,
 							ocount);
@@ -995,7 +996,7 @@
 		 */
 		buffered =3D 1;
 		pos +=3D num_written;
-		trace_printk("TPK: end unlikely(file->f_flags \& O_DIRECT) with
num_written=3D%i\n",
+		trace_printk("TPK: end unlikely(file->f_flags & O_DIRECT) with
num_written=3D%i\n",
 			     num_written);
 	}

@@ -1019,9 +1020,20 @@
 		trace_printk("TPK: start section while (iov_iter_count() > 0)\n");

 		size_t offset =3D pos & (PAGE_CACHE_SIZE - 1);
-		size_t write_bytes =3D min(iov_iter_count(&i),
-					 nrptrs * (size_t)PAGE_CACHE_SIZE -
-					 offset);
+		write_bytes =3D min(iov_iter_count(&i),
+				  nrptrs * (size_t)PAGE_CACHE_SIZE -
+				  offset);
+		if (unlikely(copied_problem)) {
+			if (copied_loop_count > 128) {
+				write_bytes =3D min(write_bytes, 4096);
+			} else if (copied_loop_count > 160) {
+				write_bytes =3D min(write_bytes, 2048);
+			} else if (copied_loop_count > 192) {
+				write_bytes =3D min(write_bytes, 1024);
+			} else if (copied_loop_count > 224) {
+				write_bytes =3D min(write_bytes, 512);
+			}
+		}
 		size_t num_pages =3D (write_bytes + offset +
 				    PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
--
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RE: [PATCH] btrfs file write debugging patch

[Zhong, Xin]

Is your system running out of memory or is there any other thread like =
flush-btrfs competing for the same page?

I can only see one process in your ftrace log. You may need to trace al=
l btrfs.ko function calls instead of a single process. Thanks!

-----Original Message-----
=46rom: linux-btrfs-owner@vger.kernel.org [mailto:linux-btrfs-owner@vge=
r.kernel.org] On Behalf Of Mitch Harder
Sent: Tuesday, March 01, 2011 4:20 AM
To: Maria Wikstr=F6m
Cc: Josef Bacik; Johannes Hirte; Chris Mason; Zhong, Xin; linux-btrfs@v=
ger.kernel.org
Subject: Re: [PATCH] btrfs file write debugging patch

2011/2/28 Mitch Harder <mitch.harder@sabayonlinux.org>:
> 2011/2/28 Maria Wikstr=F6m <maria@ponstudios.se>:
>> m=E5n 2011-02-28 klockan 11:10 -0500 skrev Josef Bacik:
>>> On Mon, Feb 28, 2011 at 11:13:59AM +0100, Johannes Hirte wrote:
>>> > On Monday 28 February 2011 02:46:05 Chris Mason wrote:
>>> > > Excerpts from Mitch Harder's message of 2011-02-25 13:43:37 -05=
00:
>>> > > > Some clarification on my previous message...
>>> > > >
>>> > > > After looking at my ftrace log more closely, I can see where =
Btrfs is
>>> > > > trying to release the allocated pages. =A0However, the calcul=
ation for
>>> > > > the number of dirty_pages is equal to 1 when "copied =3D=3D 0=
".
>>> > > >
>>> > > > So I'm seeing at least two problems:
>>> > > > (1) =A0It keeps looping when "copied =3D=3D 0".
>>> > > > (2) =A0One dirty page is not being released on every loop eve=
n though
>>> > > > "copied =3D=3D 0" (at least this problem keeps it from being =
an infinite
>>> > > > loop by eventually exhausting reserveable space on the disk).
>>> > >
>>> > > Hi everyone,
>>> > >
>>> > > There are actually tow bugs here. =A0First the one that Mitch h=
it, and a
>>> > > second one that still results in bad file_write results with my
>>> > > debugging hunks (the first two hunks below) in place.
>>> > >
>>> > > My patch fixes Mitch's bug by checking for copied =3D=3D 0 afte=
r
>>> > > btrfs_copy_from_user and going the correct delalloc accounting.=
 =A0This
>>> > > one looks solved, but you'll notice the patch is bigger.
>>> > >
>>> > > First, I add some random failures to btrfs_copy_from_user() by =
failing
>>> > > everyone once and a while. =A0This was much more reliable than =
trying to
>>> > > use memory pressure than making copy_from_user fail.
>>> > >
>>> > > If copy_from_user fails and we partially update a page, we end =
up with a
>>> > > page that may go away due to memory pressure. =A0But, btrfs_fil=
e_write
>>> > > assumes that only the first and last page may have good data th=
at needs
>>> > > to be read off the disk.
>>> > >
>>> > > This patch ditches that code and puts it into prepare_pages ins=
tead.
>>> > > But I'm still having some errors during long stress.sh runs. =A0=
Ideas are
>>> > > more than welcome, hopefully some other timezones will kick in =
ideas
>>> > > while I sleep.
>>> >
>>> > At least it doesn't fix the emerge-problem for me. The behavior i=
s now the same
>>> > as with 2.6.38-rc3. It needs a 'emerge --oneshot dev-libs/libgcry=
pt' with no
>>> > further interaction to get the emerge-process hang with a svn-pro=
cess
>>> > consuming 100% CPU. I can cancel the emerge-process with ctrl-c b=
ut the
>>> > spawned svn-process stays and it needs a reboot to get rid of it.
>>>
>>> Can you cat /proc/$pid/wchan a few times so we can get an idea of w=
here it's
>>> looping? =A0Thanks,
>>>
>>> Josef
>>
>> It behaves the same way here with btrfs-unstable.
>> The output of "cat /proc/$pid/wchan" is 0.
>>
>> // Maria
>>
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-btr=
fs" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at =A0http://vger.kernel.org/majordomo-info.htm=
l
>>>
>>
>>
>>
>
> I've applied the patch at the head of this thread (with the jiffies
> debugging commented out) and I'm attaching a ftrace using the
> function_graph tracer when I'm stuck in the loop. =A0I've just snippe=
d
> out a couple of the loops (the full trace file is quite large, and
> mostly repititious).
>
> I'm going to try to modify file.c with some trace_printk debugging to
> show the values of several of the relevant variables at various
> stages.
>
> I'm going to try to exit the loop after 256 tries with an EFAULT so I
> can stop the tracing at that point and capture a trace of the entry
> into the problem (the ftrace ring buffer fills up too fast for me to
> capture the entry point).
>

As promised, I'm put together a modified file.c with many trace_printk
debugging statements to augment the ftrace.

The trace is ~128K compressed (about 31,600 lines or 2.6MB
uncompressed), so I'm putting it up on my local server instead of
attaching.  Let me know if it would be more appropriate to send to the
list as an attachment.

http://dontpanic.dyndns.org/ftrace-btrfs-file-write-debug-v2.gz

I preface all my trace_printk comments with "TPK:" to make skipping
through the trace easier.

The trace contains the trace of about 3 or 4 successful passes through
the btrfs_file_aio_write() function to show what a successful trace
looks like.

The pass through the btrfs_file_aio_write() that breaks begins on line =
1088.

I let it loop through the while (iov_iter_count(&i) > 0) {} loop for
256 times when copied=3D=3D0 (otherwise it would loop infinitely).  The=
n
exit out and stop the trace.

=46or reference, here's a diff file for the debugging statements I've
added to file.c:

Let me know if you would like me to re-run this trial with different
debugging lines.

 fs/btrfs/file.c /usr/src/linux/fs/btrfs/file.c
--- fs/btrfs/file.c	2011-02-28 10:13:45.000000000 -0600
+++ /usr/src/linux/fs/btrfs/file.c	2011-02-28 13:07:11.000000000 -0600
@@ -53,12 +53,14 @@
 	int offset =3D pos & (PAGE_CACHE_SIZE - 1);
 	int total_copied =3D 0;

+	/***************************
 	if ((jiffies % 10) =3D=3D 0)
 		return 0;

 	if ((jiffies % 25) =3D=3D 0) {
 		write_bytes /=3D 2;
 	}
+	**************************/

 	while (write_bytes > 0) {
 		size_t count =3D min_t(size_t,
@@ -82,10 +84,13 @@

 		/* Return to btrfs_file_aio_write to fault page */
 		if (unlikely(copied =3D=3D 0)) {
+			trace_printk("TPK: unlikely copied =3D=3D 0 in btrfs_copy_from_user
(total_copied=3D%i)\n",
+				     total_copied);
 			break;
 		}

 		if (unlikely(copied < PAGE_CACHE_SIZE - offset)) {
+			trace_printk("TPK: unlikely copied < PAGE_CACHE_SIZE - offset in
btrfs_copy_from_user\n");
 			offset +=3D copied;
 		} else {
 			pg++;
@@ -910,8 +915,13 @@
 	int will_write;
 	int buffered =3D 0;
 	int copied =3D 0;
+	int copied_problem =3D 0;
+	int copied_loop_count =3D 0;
+	int stop_ftrace =3D 0;
 	int dirty_pages =3D 0;

+	trace_printk("TPK: Entering btrfs_file_aio_write()\n");
+
 	will_write =3D ((file->f_flags & O_DSYNC) || IS_SYNC(inode) ||
 		      (file->f_flags & O_DIRECT));

@@ -953,6 +963,7 @@
 	BTRFS_I(inode)->sequence++;

 	if (unlikely(file->f_flags & O_DIRECT)) {
+		trace_printk("TPK: transferred to unlikely(file->f_flags \& O_DIRECT=
)\n");
 		num_written =3D generic_file_direct_write(iocb, iov, &nr_segs,
 							pos, ppos, count,
 							ocount);
@@ -984,6 +995,8 @@
 		 */
 		buffered =3D 1;
 		pos +=3D num_written;
+		trace_printk("TPK: end unlikely(file->f_flags \& O_DIRECT) with
num_written=3D%i\n",
+			     num_written);
 	}

 	iov_iter_init(&i, iov, nr_segs, count, num_written);
@@ -1003,6 +1016,8 @@
 	last_index =3D (pos + iov_iter_count(&i)) >> PAGE_CACHE_SHIFT;

 	while (iov_iter_count(&i) > 0) {
+		trace_printk("TPK: start section while (iov_iter_count() > 0)\n");
+
 		size_t offset =3D pos & (PAGE_CACHE_SIZE - 1);
 		size_t write_bytes =3D min(iov_iter_count(&i),
 					 nrptrs * (size_t)PAGE_CACHE_SIZE -
@@ -1010,6 +1025,9 @@
 		size_t num_pages =3D (write_bytes + offset +
 				    PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;

+		trace_printk("TPK: iov_iter_count()=3D%i || nr_segs=3D%lu || nrptrs=3D=
%i
|| offset=3D%lu || write_bytes=3D%lu || num_pages=3D%lu\n",
+						iov_iter_count(&i), nr_segs, nrptrs, offset, write_bytes, num_pa=
ges);
+
 		WARN_ON(num_pages > nrptrs);
 		memset(pages, 0, sizeof(struct page *) * nrptrs);

@@ -1022,6 +1040,19 @@
 			goto out;
 		}

+		if (unlikely(copied_problem)) {
+			copied_loop_count++;
+			trace_printk("TPK: copied problem(%i)\n",
+				     copied_loop_count);
+			/* Give up if we've already tried 256 times */
+			if (copied_loop_count > 256) {
+				ret =3D -EFAULT;
+				stop_ftrace =3D 1;
+				trace_printk("TPK: copied loop count exceeded, returning EFAULT...=
=2E\n");
+				goto out;
+			}
+		}
+
 		ret =3D btrfs_delalloc_reserve_space(inode,
 					num_pages << PAGE_CACHE_SHIFT);
 		if (ret)
@@ -1045,6 +1076,10 @@
 				       PAGE_CACHE_SIZE - 1) >>
 				       PAGE_CACHE_SHIFT;

+		if (copied =3D=3D 0) {
+			copied_problem =3D 1;
+		}
+
 		if (num_pages > dirty_pages) {
 			if (copied > 0)
 				atomic_inc(
@@ -1080,11 +1115,19 @@
 		num_written +=3D copied;

 		cond_resched();
+		trace_printk("TPK: end section while (iov_iter_count() > 0)\n");
+		trace_printk(" copied=3D%i || dirty_pages=3D%i || num_written=3D%i |=
|
ending iov_iter_count=3D%i\n",
+						copied, dirty_pages, num_written, iov_iter_count(&i) );
 	}
 out:
+	trace_printk("TPK: Reached: out:\n");
+
 	mutex_unlock(&inode->i_mutex);
-	if (ret)
+	if (ret) {
 		err =3D ret;
+		trace_printk("TPK: ret,err had value %i when out: was reached
(num_written: %i)\n",
+			     ret, num_written);
+	}

 	kfree(pages);
 	*ppos =3D pos;
@@ -1140,6 +1183,19 @@
 	}
 done:
 	current->backing_dev_info =3D NULL;
+	if (ret) {
+		trace_printk("TPK: btrfs_file_aio_write exiting with non-zero ret
value (%i)\n", ret);
+		trace_printk("TPK: Returning num_written (%i) ? num_written (%i) :
err (%i) =3D %i\n",
+				num_written, num_written, err, num_written ? num_written : err);
+	} else {
+		trace_printk("TPK: btrfs_file_aio_write exiting normally with (%i)",
+			     num_written ? num_written : err);
+	}
+=09
+	if (unlikely(stop_ftrace)) {
+		tracing_off();
+	}
+
 	return num_written ? num_written : err;
 }
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RE: [PATCH] btrfs file write debugging patch

[Zhong, Xin]

Hi Mitch,

I suspect there's a lock contention between flush-btrfs (lock_dellalloc=
_pages) and btrfs_file_aio_write. However I can not recreate it locally=
=2E Could you please try below patch? Thanks!

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c index 65338a1..b9d0929 1=
00644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1007,17 +1007,16 @@ static ssize_t btrfs_file_aio_write(struct kioc=
b *iocb,
 			goto out;
 		}
=20
-		ret =3D btrfs_delalloc_reserve_space(inode,
-					num_pages << PAGE_CACHE_SHIFT);
-		if (ret)
-			goto out;
-
 		ret =3D prepare_pages(root, file, pages, num_pages,
 				    pos, first_index, last_index,
 				    write_bytes);
-		if (ret) {
-			btrfs_delalloc_release_space(inode,
+		if (ret)
+			goto out;
+	=09
+		ret =3D btrfs_delalloc_reserve_space(inode,
 					num_pages << PAGE_CACHE_SHIFT);
+		if (ret) {
+			btrfs_drop_pages(pages, num_pages);
 			goto out;
 		}


-----Original Message-----
=46rom: linux-btrfs-owner@vger.kernel.org [mailto:linux-btrfs-owner@vge=
r.kernel.org] On Behalf Of Zhong, Xin
Sent: Tuesday, March 01, 2011 6:15 PM
To: Mitch Harder; Maria Wikstr=F6m
Cc: Josef Bacik; Johannes Hirte; Chris Mason; linux-btrfs@vger.kernel.o=
rg
Subject: RE: [PATCH] btrfs file write debugging patch

Is your system running out of memory or is there any other thread like =
flush-btrfs competing for the same page?

I can only see one process in your ftrace log. You may need to trace al=
l btrfs.ko function calls instead of a single process. Thanks!

-----Original Message-----
=46rom: linux-btrfs-owner@vger.kernel.org [mailto:linux-btrfs-owner@vge=
r.kernel.org] On Behalf Of Mitch Harder
Sent: Tuesday, March 01, 2011 4:20 AM
To: Maria Wikstr=F6m
Cc: Josef Bacik; Johannes Hirte; Chris Mason; Zhong, Xin; linux-btrfs@v=
ger.kernel.org
Subject: Re: [PATCH] btrfs file write debugging patch

2011/2/28 Mitch Harder <mitch.harder@sabayonlinux.org>:
> 2011/2/28 Maria Wikstr=F6m <maria@ponstudios.se>:
>> m=E5n 2011-02-28 klockan 11:10 -0500 skrev Josef Bacik:
>>> On Mon, Feb 28, 2011 at 11:13:59AM +0100, Johannes Hirte wrote:
>>> > On Monday 28 February 2011 02:46:05 Chris Mason wrote:
>>> > > Excerpts from Mitch Harder's message of 2011-02-25 13:43:37 -05=
00:
>>> > > > Some clarification on my previous message...
>>> > > >
>>> > > > After looking at my ftrace log more closely, I can see where =
Btrfs is
>>> > > > trying to release the allocated pages. =A0However, the calcul=
ation for
>>> > > > the number of dirty_pages is equal to 1 when "copied =3D=3D 0=
".
>>> > > >
>>> > > > So I'm seeing at least two problems:
>>> > > > (1) =A0It keeps looping when "copied =3D=3D 0".
>>> > > > (2) =A0One dirty page is not being released on every loop eve=
n though
>>> > > > "copied =3D=3D 0" (at least this problem keeps it from being =
an infinite
>>> > > > loop by eventually exhausting reserveable space on the disk).
>>> > >
>>> > > Hi everyone,
>>> > >
>>> > > There are actually tow bugs here. =A0First the one that Mitch h=
it, and a
>>> > > second one that still results in bad file_write results with my
>>> > > debugging hunks (the first two hunks below) in place.
>>> > >
>>> > > My patch fixes Mitch's bug by checking for copied =3D=3D 0 afte=
r
>>> > > btrfs_copy_from_user and going the correct delalloc accounting.=
 =A0This
>>> > > one looks solved, but you'll notice the patch is bigger.
>>> > >
>>> > > First, I add some random failures to btrfs_copy_from_user() by =
failing
>>> > > everyone once and a while. =A0This was much more reliable than =
trying to
>>> > > use memory pressure than making copy_from_user fail.
>>> > >
>>> > > If copy_from_user fails and we partially update a page, we end =
up with a
>>> > > page that may go away due to memory pressure. =A0But, btrfs_fil=
e_write
>>> > > assumes that only the first and last page may have good data th=
at needs
>>> > > to be read off the disk.
>>> > >
>>> > > This patch ditches that code and puts it into prepare_pages ins=
tead.
>>> > > But I'm still having some errors during long stress.sh runs. =A0=
Ideas are
>>> > > more than welcome, hopefully some other timezones will kick in =
ideas
>>> > > while I sleep.
>>> >
>>> > At least it doesn't fix the emerge-problem for me. The behavior i=
s now the same
>>> > as with 2.6.38-rc3. It needs a 'emerge --oneshot dev-libs/libgcry=
pt' with no
>>> > further interaction to get the emerge-process hang with a svn-pro=
cess
>>> > consuming 100% CPU. I can cancel the emerge-process with ctrl-c b=
ut the
>>> > spawned svn-process stays and it needs a reboot to get rid of it.
>>>
>>> Can you cat /proc/$pid/wchan a few times so we can get an idea of w=
here it's
>>> looping? =A0Thanks,
>>>
>>> Josef
>>
>> It behaves the same way here with btrfs-unstable.
>> The output of "cat /proc/$pid/wchan" is 0.
>>
>> // Maria
>>
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe linux-btr=
fs" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at =A0http://vger.kernel.org/majordomo-info.htm=
l
>>>
>>
>>
>>
>
> I've applied the patch at the head of this thread (with the jiffies
> debugging commented out) and I'm attaching a ftrace using the
> function_graph tracer when I'm stuck in the loop. =A0I've just snippe=
d
> out a couple of the loops (the full trace file is quite large, and
> mostly repititious).
>
> I'm going to try to modify file.c with some trace_printk debugging to
> show the values of several of the relevant variables at various
> stages.
>
> I'm going to try to exit the loop after 256 tries with an EFAULT so I
> can stop the tracing at that point and capture a trace of the entry
> into the problem (the ftrace ring buffer fills up too fast for me to
> capture the entry point).
>

As promised, I'm put together a modified file.c with many trace_printk
debugging statements to augment the ftrace.

The trace is ~128K compressed (about 31,600 lines or 2.6MB
uncompressed), so I'm putting it up on my local server instead of
attaching.  Let me know if it would be more appropriate to send to the
list as an attachment.

http://dontpanic.dyndns.org/ftrace-btrfs-file-write-debug-v2.gz

I preface all my trace_printk comments with "TPK:" to make skipping
through the trace easier.

The trace contains the trace of about 3 or 4 successful passes through
the btrfs_file_aio_write() function to show what a successful trace
looks like.

The pass through the btrfs_file_aio_write() that breaks begins on line =
1088.

I let it loop through the while (iov_iter_count(&i) > 0) {} loop for
256 times when copied=3D=3D0 (otherwise it would loop infinitely).  The=
n
exit out and stop the trace.

=46or reference, here's a diff file for the debugging statements I've
added to file.c:

Let me know if you would like me to re-run this trial with different
debugging lines.

 fs/btrfs/file.c /usr/src/linux/fs/btrfs/file.c
--- fs/btrfs/file.c	2011-02-28 10:13:45.000000000 -0600
+++ /usr/src/linux/fs/btrfs/file.c	2011-02-28 13:07:11.000000000 -0600
@@ -53,12 +53,14 @@
 	int offset =3D pos & (PAGE_CACHE_SIZE - 1);
 	int total_copied =3D 0;

+	/***************************
 	if ((jiffies % 10) =3D=3D 0)
 		return 0;

 	if ((jiffies % 25) =3D=3D 0) {
 		write_bytes /=3D 2;
 	}
+	**************************/

 	while (write_bytes > 0) {
 		size_t count =3D min_t(size_t,
@@ -82,10 +84,13 @@

 		/* Return to btrfs_file_aio_write to fault page */
 		if (unlikely(copied =3D=3D 0)) {
+			trace_printk("TPK: unlikely copied =3D=3D 0 in btrfs_copy_from_user
(total_copied=3D%i)\n",
+				     total_copied);
 			break;
 		}

 		if (unlikely(copied < PAGE_CACHE_SIZE - offset)) {
+			trace_printk("TPK: unlikely copied < PAGE_CACHE_SIZE - offset in
btrfs_copy_from_user\n");
 			offset +=3D copied;
 		} else {
 			pg++;
@@ -910,8 +915,13 @@
 	int will_write;
 	int buffered =3D 0;
 	int copied =3D 0;
+	int copied_problem =3D 0;
+	int copied_loop_count =3D 0;
+	int stop_ftrace =3D 0;
 	int dirty_pages =3D 0;

+	trace_printk("TPK: Entering btrfs_file_aio_write()\n");
+
 	will_write =3D ((file->f_flags & O_DSYNC) || IS_SYNC(inode) ||
 		      (file->f_flags & O_DIRECT));

@@ -953,6 +963,7 @@
 	BTRFS_I(inode)->sequence++;

 	if (unlikely(file->f_flags & O_DIRECT)) {
+		trace_printk("TPK: transferred to unlikely(file->f_flags \& O_DIRECT=
)\n");
 		num_written =3D generic_file_direct_write(iocb, iov, &nr_segs,
 							pos, ppos, count,
 							ocount);
@@ -984,6 +995,8 @@
 		 */
 		buffered =3D 1;
 		pos +=3D num_written;
+		trace_printk("TPK: end unlikely(file->f_flags \& O_DIRECT) with
num_written=3D%i\n",
+			     num_written);
 	}

 	iov_iter_init(&i, iov, nr_segs, count, num_written);
@@ -1003,6 +1016,8 @@
 	last_index =3D (pos + iov_iter_count(&i)) >> PAGE_CACHE_SHIFT;

 	while (iov_iter_count(&i) > 0) {
+		trace_printk("TPK: start section while (iov_iter_count() > 0)\n");
+
 		size_t offset =3D pos & (PAGE_CACHE_SIZE - 1);
 		size_t write_bytes =3D min(iov_iter_count(&i),
 					 nrptrs * (size_t)PAGE_CACHE_SIZE -
@@ -1010,6 +1025,9 @@
 		size_t num_pages =3D (write_bytes + offset +
 				    PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;

+		trace_printk("TPK: iov_iter_count()=3D%i || nr_segs=3D%lu || nrptrs=3D=
%i
|| offset=3D%lu || write_bytes=3D%lu || num_pages=3D%lu\n",
+						iov_iter_count(&i), nr_segs, nrptrs, offset, write_bytes, num_pa=
ges);
+
 		WARN_ON(num_pages > nrptrs);
 		memset(pages, 0, sizeof(struct page *) * nrptrs);

@@ -1022,6 +1040,19 @@
 			goto out;
 		}

+		if (unlikely(copied_problem)) {
+			copied_loop_count++;
+			trace_printk("TPK: copied problem(%i)\n",
+				     copied_loop_count);
+			/* Give up if we've already tried 256 times */
+			if (copied_loop_count > 256) {
+				ret =3D -EFAULT;
+				stop_ftrace =3D 1;
+				trace_printk("TPK: copied loop count exceeded, returning EFAULT...=
=2E\n");
+				goto out;
+			}
+		}
+
 		ret =3D btrfs_delalloc_reserve_space(inode,
 					num_pages << PAGE_CACHE_SHIFT);
 		if (ret)
@@ -1045,6 +1076,10 @@
 				       PAGE_CACHE_SIZE - 1) >>
 				       PAGE_CACHE_SHIFT;

+		if (copied =3D=3D 0) {
+			copied_problem =3D 1;
+		}
+
 		if (num_pages > dirty_pages) {
 			if (copied > 0)
 				atomic_inc(
@@ -1080,11 +1115,19 @@
 		num_written +=3D copied;

 		cond_resched();
+		trace_printk("TPK: end section while (iov_iter_count() > 0)\n");
+		trace_printk(" copied=3D%i || dirty_pages=3D%i || num_written=3D%i |=
|
ending iov_iter_count=3D%i\n",
+						copied, dirty_pages, num_written, iov_iter_count(&i) );
 	}
 out:
+	trace_printk("TPK: Reached: out:\n");
+
 	mutex_unlock(&inode->i_mutex);
-	if (ret)
+	if (ret) {
 		err =3D ret;
+		trace_printk("TPK: ret,err had value %i when out: was reached
(num_written: %i)\n",
+			     ret, num_written);
+	}

 	kfree(pages);
 	*ppos =3D pos;
@@ -1140,6 +1183,19 @@
 	}
 done:
 	current->backing_dev_info =3D NULL;
+	if (ret) {
+		trace_printk("TPK: btrfs_file_aio_write exiting with non-zero ret
value (%i)\n", ret);
+		trace_printk("TPK: Returning num_written (%i) ? num_written (%i) :
err (%i) =3D %i\n",
+				num_written, num_written, err, num_written ? num_written : err);
+	} else {
+		trace_printk("TPK: btrfs_file_aio_write exiting normally with (%i)",
+			     num_written ? num_written : err);
+	}
+=09
+	if (unlikely(stop_ftrace)) {
+		tracing_off();
+	}
+
 	return num_written ? num_written : err;
 }
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Re: [PATCH] btrfs file write debugging patch

[Mitch Harder]

On Tue, Mar 1, 2011 at 4:14 AM, Zhong, Xin <xin.zhong@intel.com> wrote:
> Is your system running out of memory or is there any other thread like flush-btrfs competing for the same page?
>

There's no sign of memory pressure.  Although I only have 1 GB in this
box, I'm still show ~1/2 GB RAM free during this build.  There's no
swap space allocated, and nothing in dmesg that indicates there's a
transient spike of RAM pressure.

> I can only see one process in your ftrace log. You may need to trace all btrfs.ko function calls instead of a single process. Thanks!
>

That ftrace.log was run with ftrace defaults for a function trace.  It
should collect calls from the whole system.

For the sake of consistency, I am intentionally trying to insure that
very few other things are going on at the same time as this build.
And I'm building with "-j1" so things will happen the same way each
time.

Also, I supplied just the tail end of the trace log.  The full log
shows a few of the other build processes leading up to the problem,
but the ftrace ring buffer fills up surprisingly fast.  Even with a
50MB ring buffer for ftrace, I usually collect less than 1 second of
information when something busy like a build is going on.

Let me know if you'd like to see the full log.  It's bigger, but I can
find someplace to put it.

But I'm pretty sure that wmldbcreate is the only thing that is going
on when the breakage occurs.  Otherwise I wouldn't get such consistent
breakage in the same spot every time.

Re: [PATCH] btrfs file write debugging patch

[Mitch Harder]

On Tue, Mar 1, 2011 at 5:56 AM, Zhong, Xin <xin.zhong@intel.com> wrote:
> Hi Mitch,
>
> I suspect there's a lock contention between flush-btrfs (lock_dellall=
oc_pages) and btrfs_file_aio_write. However I can not recreate it local=
ly. Could you please try below patch? Thanks!
>
> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c index 65338a1..b9d0929=
 100644
> --- a/fs/btrfs/file.c
> +++ b/fs/btrfs/file.c
> @@ -1007,17 +1007,16 @@ static ssize_t btrfs_file_aio_write(struct ki=
ocb *iocb,
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0goto out;
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0}
>
> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 ret =3D btrfs_delalloc_reserve_space(in=
ode,
> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0 num_pages << PAGE_CACHE_SHIFT);
> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (ret)
> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 goto out;
> -
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0ret =3D prepare_pages(root, file, page=
s, num_pages,
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
pos, first_index, last_index,
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
write_bytes);
> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (ret) {
> - =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 btrfs_delalloc_release_=
space(inode,
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (ret)
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 goto out;
> +
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 ret =3D btrfs_delalloc_reserve_space(in=
ode,
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=
 =A0 =A0num_pages << PAGE_CACHE_SHIFT);
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (ret) {
> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 btrfs_drop_pages(pages,=
 num_pages);
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0goto out;
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0}
>
>

Thanks.

I've tested this patch, but the build is still failing at the same
point as before.
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Re: [PATCH] btrfs file write debugging patch

[Piotr Szymaniak]

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On Mon, Feb 28, 2011 at 02:20:22PM -0600, Mitch Harder wrote:
> As promised, I'm put together a modified file.c with many trace_printk
> debugging statements to augment the ftrace.
> *snip*

Just my few cents. I've applied the patch from Chris Mason (Sun, 27 Feb
2011 20:46:05 -0500) and this one from Mitch (Mon, 28 Feb 2011 14:20:22
-0600) on top of vanilla 2.6.38-rc6 and it seems that it resolves my
issues with hanging `svn info' during libgcrypt emerge.

Piotr Szymaniak.
-- 
 - (...) Nie wyobrazam sobie, co ta gora miesa moglaby ci dac, czego ja
nie   moglbym   ofiarowac.  Oczywiscie  poza  piecdziesiecioma  funtami
rozrosnietych miesni.
 - Moze mnie wlasnie pociagaja rozrosniete miesnie. (...) W koncu wielu
mezczyzn pociaga rozrosnieta tkanka tluszczowa piersi.
  -- Graham Masterton, "The Wells of Hell"

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