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ext4: fix a race in the ext4 shutdown path

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This patch fixes a race between the shutdown path and bio completion
handling. In the ext4 direct io path with async io, after submitting a
bio to the block layer, if journal starting fails,
ext4_direct_IO_write() would bail out pretending that the IO
failed. The caller would have had no way of knowing whether or not the
IO was successfully submitted. So instead, we return -EIOCBQUEUED in
this case. Now, the caller knows that the IO was submitted.  The bio
completion handler takes care of the error.

Tested: Ran the shutdown xfstest test 461 in loop for over 2 hours across
4 machines resulting in over 400 runs. Verified that the race didn't
occur. Usually the race was seen in about 20-30 iterations.

Signed-off-by: Harshad Shirwadkar <harshads@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org
This commit is contained in:
Harshad Shirwadkar 2018-01-10 00:13:13 -05:00 committed by Theodore Ts'o
parent 9ee93ba3c4
commit abbc3f9395
1 changed files with 12 additions and 4 deletions
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16
fs/ext4/inode.c
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@ -3767,10 +3767,18 @@ static ssize_t ext4_direct_IO_write(struct kiocb *iocb, struct iov_iter *iter)
/* Credits for sb + inode write */
handle = ext4_journal_start(inode, EXT4_HT_INODE, 2);
if (IS_ERR(handle)) {
/* This is really bad luck. We've written the data
* but cannot extend i_size. Bail out and pretend
* the write failed... */
ret = PTR_ERR(handle);
/*
* We wrote the data but cannot extend
* i_size. Bail out. In async io case, we do
* not return error here because we have
* already submmitted the corresponding
* bio. Returning error here makes the caller
* think that this IO is done and failed
* resulting in race with bio's completion
* handler.
*/
if (!ret)
ret = PTR_ERR(handle);
if (inode->i_nlink)
ext4_orphan_del(NULL, inode);