[PATCH RESEND v3 0/3] direct-io: clean up error paths of do_blockdev_direct_IO

[PATCH RESEND v3 0/3] direct-io: clean up error paths of do_blockdev_direct_IO

[Gabriel Krisman Bertazi]

Hi Al,

This might have felt through the cracks, as I haven't seen it popup in
any trees, so I'm resending it.  No changes from the original
submission, apart from picking up the reviewed-bys.

Would you kindly consider pulling it for the next merge window?

Thanks,

Archive:
  v1: https://lkml.org/lkml/2020/9/14/915
  v2: https://www.spinics.net/lists/linux-fsdevel/msg177220.html
  v3: https://www.spinics.net/lists/linux-fsdevel/msg177310.html


Gabriel Krisman Bertazi (3):
  direct-io: clean up error paths of do_blockdev_direct_IO
  direct-io: don't force writeback for reads beyond EOF
  direct-io: defer alignment check until after the EOF check

 fs/direct-io.c | 69 ++++++++++++++++++++++----------------------------
 1 file changed, 30 insertions(+), 39 deletions(-)

-- 
2.28.0

[PATCH RESEND v3 1/3] direct-io: clean up error paths of do_blockdev_direct_IO

[Gabriel Krisman Bertazi]

In preparation to resort DIO checks, reduce code duplication of error
handling in do_blockdev_direct_IO.

Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
---
 fs/direct-io.c | 35 ++++++++++++++---------------------
 1 file changed, 14 insertions(+), 21 deletions(-)

diff --git a/fs/direct-io.c b/fs/direct-io.c
index 183299892465..6c11db1cec27 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -1170,7 +1170,7 @@ do_blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
 			blkbits = blksize_bits(bdev_logical_block_size(bdev));
 		blocksize_mask = (1 << blkbits) - 1;
 		if (align & blocksize_mask)
-			goto out;
+			return -EINVAL;
 	}
 
 	/* watch out for a 0 len io from a tricksy fs */
@@ -1178,9 +1178,8 @@ do_blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
 		return 0;
 
 	dio = kmem_cache_alloc(dio_cache, GFP_KERNEL);
-	retval = -ENOMEM;
 	if (!dio)
-		goto out;
+		return -ENOMEM;
 	/*
 	 * Believe it or not, zeroing out the page array caused a .5%
 	 * performance regression in a database benchmark.  So, we take
@@ -1199,22 +1198,16 @@ do_blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
 
 			retval = filemap_write_and_wait_range(mapping, offset,
 							      end - 1);
-			if (retval) {
-				inode_unlock(inode);
-				kmem_cache_free(dio_cache, dio);
-				goto out;
-			}
+			if (retval)
+				goto fail_dio;
 		}
 	}
 
 	/* Once we sampled i_size check for reads beyond EOF */
 	dio->i_size = i_size_read(inode);
 	if (iov_iter_rw(iter) == READ && offset >= dio->i_size) {
-		if (dio->flags & DIO_LOCKING)
-			inode_unlock(inode);
-		kmem_cache_free(dio_cache, dio);
 		retval = 0;
-		goto out;
+		goto fail_dio;
 	}
 
 	/*
@@ -1258,14 +1251,8 @@ do_blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
 			 */
 			retval = sb_init_dio_done_wq(dio->inode->i_sb);
 		}
-		if (retval) {
-			/*
-			 * We grab i_mutex only for reads so we don't have
-			 * to release it here
-			 */
-			kmem_cache_free(dio_cache, dio);
-			goto out;
-		}
+		if (retval)
+			goto fail_dio;
 	}
 
 	/*
@@ -1368,7 +1355,13 @@ do_blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
 	} else
 		BUG_ON(retval != -EIOCBQUEUED);
 
-out:
+	return retval;
+
+fail_dio:
+	if (dio->flags & DIO_LOCKING && iov_iter_rw(iter) == READ)
+		inode_unlock(inode);
+
+	kmem_cache_free(dio_cache, dio);
 	return retval;
 }
 
-- 
2.28.0

[PATCH RESEND v3 2/3] direct-io: don't force writeback for reads beyond EOF

[Gabriel Krisman Bertazi]

If a DIO read starts past EOF, the kernel won't attempt it, so we don't
need to flush dirty pages before failing the syscall.

Suggested-by: Jan Kara <jack@suse.cz>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
---
 fs/direct-io.c | 24 +++++++++++-------------
 1 file changed, 11 insertions(+), 13 deletions(-)

diff --git a/fs/direct-io.c b/fs/direct-io.c
index 6c11db1cec27..c17efe58f1c9 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -1188,19 +1188,9 @@ do_blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
 	memset(dio, 0, offsetof(struct dio, pages));
 
 	dio->flags = flags;
-	if (dio->flags & DIO_LOCKING) {
-		if (iov_iter_rw(iter) == READ) {
-			struct address_space *mapping =
-					iocb->ki_filp->f_mapping;
-
-			/* will be released by direct_io_worker */
-			inode_lock(inode);
-
-			retval = filemap_write_and_wait_range(mapping, offset,
-							      end - 1);
-			if (retval)
-				goto fail_dio;
-		}
+	if (dio->flags & DIO_LOCKING && iov_iter_rw(iter) == READ) {
+		/* will be released by direct_io_worker */
+		inode_lock(inode);
 	}
 
 	/* Once we sampled i_size check for reads beyond EOF */
@@ -1210,6 +1200,14 @@ do_blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
 		goto fail_dio;
 	}
 
+	if (dio->flags & DIO_LOCKING && iov_iter_rw(iter) == READ) {
+		struct address_space *mapping = iocb->ki_filp->f_mapping;
+
+		retval = filemap_write_and_wait_range(mapping, offset, end - 1);
+		if (retval)
+			goto fail_dio;
+	}
+
 	/*
 	 * For file extending writes updating i_size before data writeouts
 	 * complete can expose uninitialized blocks in dumb filesystems.
-- 
2.28.0

[PATCH RESEND v3 3/3] direct-io: defer alignment check until after the EOF check

[Gabriel Krisman Bertazi]

Prior to commit 9fe55eea7e4b ("Fix race when checking i_size on direct
i/o read"), an unaligned direct read past end of file would trigger EOF,
since generic_file_aio_read detected this read-at-EOF condition and
skipped the direct IO read entirely, returning 0. After that change, the
read now reaches dio_generic, which detects the misalignment and returns
EINVAL.

This consolidates the generic direct-io to follow the same behavior of
filesystems.  Apparently, this fix will only affect ocfs2 since other
filesystems do this verification before calling do_blockdev_direct_IO,
with the exception of f2fs, which has the same bug, but is fixed in the
next patch.

it can be verified by a read loop on a file that does a partial read
before EOF (On file that doesn't end at an aligned address).  The
following code fails on an unaligned file on filesystems without
prior validation without this patch, but not on btrfs, ext4, and xfs.

  while (done < total) {
    ssize_t delta = pread(fd, buf + done, total - done, off + done);
    if (!delta)
      break;
    ...
  }

Fix this regression by moving the misalignment check to after the EOF
check added by commit 74cedf9b6c60 ("direct-io: Fix negative return from
dio read beyond eof").

Based on a patch by Jamie Liu.

Reported-by: Jamie Liu <jamieliu@google.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
---
 fs/direct-io.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/fs/direct-io.c b/fs/direct-io.c
index c17efe58f1c9..82838cca934b 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -1165,14 +1165,6 @@ do_blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
 	 * the early prefetch in the caller enough time.
 	 */
 
-	if (align & blocksize_mask) {
-		if (bdev)
-			blkbits = blksize_bits(bdev_logical_block_size(bdev));
-		blocksize_mask = (1 << blkbits) - 1;
-		if (align & blocksize_mask)
-			return -EINVAL;
-	}
-
 	/* watch out for a 0 len io from a tricksy fs */
 	if (iov_iter_rw(iter) == READ && !count)
 		return 0;
@@ -1200,6 +1192,14 @@ do_blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
 		goto fail_dio;
 	}
 
+	if (align & blocksize_mask) {
+		if (bdev)
+			blkbits = blksize_bits(bdev_logical_block_size(bdev));
+		blocksize_mask = (1 << blkbits) - 1;
+		if (align & blocksize_mask)
+			goto fail_dio;
+	}
+
 	if (dio->flags & DIO_LOCKING && iov_iter_rw(iter) == READ) {
 		struct address_space *mapping = iocb->ki_filp->f_mapping;
 
-- 
2.28.0