[PATCH 1/3] ext4: fix COLLAPSE_RANGE failure issue on ext4 with 1KB block size

[PATCH 1/3] ext4: fix COLLAPSE_RANGE failure issue on ext4 with 1KB block size

[Namjae Jeon]

From: Namjae Jeon <namjae.jeon@samsung.com>

When formatting with 1KB or 2KB(not aligned with PAGE SIZE) block size,
xfstests generic/075 and 091 are failing. The offset supplied to function
truncate_pagecache_range is block size aligned. In this function start offset
is re-aligned to PAGE_SIZE by rounding_up to the next page boundary.
Due to this rounding up, old data remains in the page cache when blocksize is
less than page size and start offset is not aligned with page size.
In case of collapse range, we need to align start offset to page size boundary
by doing a round down operation instead of round up.

Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Ashish Sangwan <a.sangwan@samsung.com>
---
 fs/ext4/extents.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 1bb3e4b..f386dd6 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -5404,8 +5404,8 @@ int ext4_collapse_range(struct inode *inode, loff_t offset, loff_t len)
 	struct super_block *sb = inode->i_sb;
 	ext4_lblk_t punch_start, punch_stop;
 	handle_t *handle;
-	unsigned int credits;
-	loff_t new_size;
+	unsigned int credits, rounding;
+	loff_t new_size, ioffset;
 	int ret;
 
 	/* Collapse range works only on fs block size aligned offsets. */
@@ -5428,8 +5428,11 @@ int ext4_collapse_range(struct inode *inode, loff_t offset, loff_t len)
 			return ret;
 	}
 
+	rounding = max_t(uint, 1 << EXT4_BLOCK_SIZE_BITS(sb), PAGE_CACHE_SIZE);
+	ioffset = offset & ~(rounding - 1);
+
 	/* Write out all dirty pages */
-	ret = filemap_write_and_wait_range(inode->i_mapping, offset, -1);
+	ret = filemap_write_and_wait_range(inode->i_mapping, ioffset, -1);
 	if (ret)
 		return ret;
 
@@ -5451,7 +5454,7 @@ int ext4_collapse_range(struct inode *inode, loff_t offset, loff_t len)
 		goto out_mutex;
 	}
 
-	truncate_pagecache_range(inode, offset, -1);
+	truncate_pagecache_range(inode, ioffset, -1);
 
 	/* Wait for existing dio to complete */
 	ext4_inode_block_unlocked_dio(inode);
-- 
1.7.11-rc0

Re: [PATCH 1/3] ext4: fix COLLAPSE_RANGE failure issue on ext4 with 1KB block size

[Lukáš Czerner]

[-- Attachment #1: Type: TEXT/PLAIN, Size: 3162 bytes --]

On Thu, 17 Apr 2014, Namjae Jeon wrote:

> Date: Thu, 17 Apr 2014 07:27:45 +0900
> From: Namjae Jeon <namjae.jeon@samsung.com>
> To: Theodore Ts'o <tytso@mit.edu>
> Cc: linux-ext4 <linux-ext4@vger.kernel.org>,
>     'Lukáš Czerner' <lczerner@redhat.com>
> Subject: [PATCH 1/3] ext4: fix COLLAPSE_RANGE failure issue on ext4 with 1KB
>     block size
> 
> From: Namjae Jeon <namjae.jeon@samsung.com>
> 
> When formatting with 1KB or 2KB(not aligned with PAGE SIZE) block size,
> xfstests generic/075 and 091 are failing. The offset supplied to function
> truncate_pagecache_range is block size aligned. In this function start offset
> is re-aligned to PAGE_SIZE by rounding_up to the next page boundary.
> Due to this rounding up, old data remains in the page cache when blocksize is
> less than page size and start offset is not aligned with page size.
> In case of collapse range, we need to align start offset to page size boundary
> by doing a round down operation instead of round up.

Great, thanks for finding it.

> 
> Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
> Signed-off-by: Ashish Sangwan <a.sangwan@samsung.com>
> ---
>  fs/ext4/extents.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 1bb3e4b..f386dd6 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -5404,8 +5404,8 @@ int ext4_collapse_range(struct inode *inode, loff_t offset, loff_t len)
>  	struct super_block *sb = inode->i_sb;
>  	ext4_lblk_t punch_start, punch_stop;
>  	handle_t *handle;
> -	unsigned int credits;
> -	loff_t new_size;
> +	unsigned int credits, rounding;
> +	loff_t new_size, ioffset;
>  	int ret;
>  
>  	/* Collapse range works only on fs block size aligned offsets. */
> @@ -5428,8 +5428,11 @@ int ext4_collapse_range(struct inode *inode, loff_t offset, loff_t len)
>  			return ret;
>  	}
>  
> +	rounding = max_t(uint, 1 << EXT4_BLOCK_SIZE_BITS(sb), PAGE_CACHE_SIZE);
> +	ioffset = offset & ~(rounding - 1);

That looks like you're expecting that block size might be bigger
than page size. That's definitely not the case at the moment as we
can not have block size > page size. There is a discussion to
support this in the future, but even when the infrastructure is done
we would have to revisit the code anyway. So I do not think this is
needed. Just always round it down to PAGE_SIZE (since that's what
truncate_pagecache is actually using)

> +
>  	/* Write out all dirty pages */
> -	ret = filemap_write_and_wait_range(inode->i_mapping, offset, -1);
> +	ret = filemap_write_and_wait_range(inode->i_mapping, ioffset, -1);
>  	if (ret)
>  		return ret;
>  
> @@ -5451,7 +5454,7 @@ int ext4_collapse_range(struct inode *inode, loff_t offset, loff_t len)
>  		goto out_mutex;
>  	}
>  
> -	truncate_pagecache_range(inode, offset, -1);
> +	truncate_pagecache_range(inode, ioffset, -1);

As I mentioned in a different email we can just use
truncate_pagecache(). In fact we should use it because we want to
remove private COWed pages as well I think.

Thanks!
-Lukas

>  
>  	/* Wait for existing dio to complete */
>  	ext4_inode_block_unlocked_dio(inode);
> 

RE: [PATCH 1/3] ext4: fix COLLAPSE_RANGE failure issue on ext4 with 1KB block size

[Namjae Jeon]

> On Thu, 17 Apr 2014, Namjae Jeon wrote:
> 
> > Date: Thu, 17 Apr 2014 07:27:45 +0900
> > From: Namjae Jeon <namjae.jeon@samsung.com>
> > To: Theodore Ts'o <tytso@mit.edu>
> > Cc: linux-ext4 <linux-ext4@vger.kernel.org>,
> >     'Lukáš Czerner' <lczerner@redhat.com>
> > Subject: [PATCH 1/3] ext4: fix COLLAPSE_RANGE failure issue on ext4 with 1KB
> >     block size
> >
> > From: Namjae Jeon <namjae.jeon@samsung.com>
> >
> > When formatting with 1KB or 2KB(not aligned with PAGE SIZE) block size,
> > xfstests generic/075 and 091 are failing. The offset supplied to function
> > truncate_pagecache_range is block size aligned. In this function start offset
> > is re-aligned to PAGE_SIZE by rounding_up to the next page boundary.
> > Due to this rounding up, old data remains in the page cache when blocksize is
> > less than page size and start offset is not aligned with page size.
> > In case of collapse range, we need to align start offset to page size boundary
> > by doing a round down operation instead of round up.
> 
> Great, thanks for finding it.
> 
> >
> > Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
> > Signed-off-by: Ashish Sangwan <a.sangwan@samsung.com>
> > ---
> >  fs/ext4/extents.c | 11 +++++++----
> >  1 file changed, 7 insertions(+), 4 deletions(-)
> >
> > diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> > index 1bb3e4b..f386dd6 100644
> > --- a/fs/ext4/extents.c
> > +++ b/fs/ext4/extents.c
> > @@ -5404,8 +5404,8 @@ int ext4_collapse_range(struct inode *inode, loff_t offset, loff_t len)
> >  	struct super_block *sb = inode->i_sb;
> >  	ext4_lblk_t punch_start, punch_stop;
> >  	handle_t *handle;
> > -	unsigned int credits;
> > -	loff_t new_size;
> > +	unsigned int credits, rounding;
> > +	loff_t new_size, ioffset;
> >  	int ret;
> >
> >  	/* Collapse range works only on fs block size aligned offsets. */
> > @@ -5428,8 +5428,11 @@ int ext4_collapse_range(struct inode *inode, loff_t offset, loff_t len)
> >  			return ret;
> >  	}
> >
> > +	rounding = max_t(uint, 1 << EXT4_BLOCK_SIZE_BITS(sb), PAGE_CACHE_SIZE);
> > +	ioffset = offset & ~(rounding - 1);
> 
> That looks like you're expecting that block size might be bigger
> than page size. That's definitely not the case at the moment as we
> can not have block size > page size. There is a discussion to
> support this in the future, but even when the infrastructure is done
> we would have to revisit the code anyway. So I do not think this is
> needed. Just always round it down to PAGE_SIZE (since that's what
> truncate_pagecache is actually using)
Right :), I will change it.

> 
> > +
> >  	/* Write out all dirty pages */
> > -	ret = filemap_write_and_wait_range(inode->i_mapping, offset, -1);
> > +	ret = filemap_write_and_wait_range(inode->i_mapping, ioffset, -1);
> >  	if (ret)
> >  		return ret;
> >
> > @@ -5451,7 +5454,7 @@ int ext4_collapse_range(struct inode *inode, loff_t offset, loff_t len)
> >  		goto out_mutex;
> >  	}
> >
> > -	truncate_pagecache_range(inode, offset, -1);
> > +	truncate_pagecache_range(inode, ioffset, -1);
> 
> As I mentioned in a different email we can just use
> truncate_pagecache(). In fact we should use it because we want to
> remove private COWed pages as well I think.
Okay, If you send the updated your patch, I will create the patch base on your patch again.

Thanks :)
> 
> Thanks!
> -Lukas
> 
> >
> >  	/* Wait for existing dio to complete */
> >  	ext4_inode_block_unlocked_dio(inode);
> >

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