From: harshads Subject: [PATCH] ext4: Fix a race in the ext4 shutdown path. Date: Tue, 9 Jan 2018 14:52:57 -0800 Message-ID: <20180109225257.93785-1-harshads@google.com> Cc: tytso@mit.edu, harshads To: linux-ext4@vger.kernel.org Return-path: Received: from mail-pg0-f66.google.com ([74.125.83.66]:40325 "EHLO mail-pg0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752178AbeAIWx1 (ORCPT ); Tue, 9 Jan 2018 17:53:27 -0500 Received: by mail-pg0-f66.google.com with SMTP id q12so9043230pgt.7 for ; Tue, 09 Jan 2018 14:53:27 -0800 (PST) Sender: linux-ext4-owner@vger.kernel.org List-ID: 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 --- fs/ext4/inode.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) 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); -- 2.16.0.rc1.238.g530d649a79-goog