Commit abbc3f93 authored Jan 10, 2018 by Harshad Shirwadkar Committed by Theodore Ts'o Jan 10, 2018

ext4: fix a race in the ext4 shutdown path



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

parent 9ee93ba3

fs/ext4/inode.c

+12 −4

Original line number	Diff line number	Diff line
		@@ -3767,9 +3767,17 @@ 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... */
		/*
		* 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);

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