linux-ext4 - [PATCH] ext4: fix off-by-one error when writing back pages before dio read

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Message-Id: <20170523013441.49030-1-ebiggers3@gmail.com>
Date:   Mon, 22 May 2017 18:34:41 -0700
From:   Eric Biggers <ebiggers3@...il.com>
To:     linux-ext4@...r.kernel.org
Cc:     Theodore Ts'o <tytso@....edu>, Jan Kara <jack@...e.com>,
        Eric Biggers <ebiggers@...gle.com>
Subject: [PATCH] ext4: fix off-by-one error when writing back pages before dio read

From: Eric Biggers <ebiggers@...gle.com>

The 'lend' argument of filemap_write_and_wait_range() is inclusive, so
we need to subtract 1 from pos + count.

Note that 'count' is guaranteed to be nonzero since
ext4_file_read_iter() returns early when given a 0 count.

Fixes: 16c54688592c ("ext4: Allow parallel DIO reads")
Signed-off-by: Eric Biggers <ebiggers@...gle.com>
---
 fs/ext4/inode.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 7c6e715b4d2e..3080ea82dd6d 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3710,7 +3710,7 @@ static ssize_t ext4_direct_IO_read(struct kiocb *iocb, struct iov_iter *iter)
 	 */
 	inode_lock_shared(inode);
 	ret = filemap_write_and_wait_range(mapping, iocb->ki_pos,
-					   iocb->ki_pos + count);
+					   iocb->ki_pos + count - 1);
 	if (ret)
 		goto out_unlock;
 	ret = __blockdev_direct_IO(iocb, inode, inode->i_sb->s_bdev,
-- 
2.13.0.219.gdb65acc882-goog