The patch below does not apply to the 4.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From abbc3f9395c76d554a9ed27d4b1ebfb5d9b0e4ca Mon Sep 17 00:00:00 2001
From: Harshad Shirwadkar harshads@google.com Date: Wed, 10 Jan 2018 00:13:13 -0500 Subject: [PATCH] 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
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index 534a9130f625..4c2f8b57bdc7 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -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);