| From 646caa9c8e196880b41cd3e3d33a2ebc752bdb85 Mon Sep 17 00:00:00 2001 |
| From: Jan Kara <jack@suse.cz> |
| Date: Mon, 4 Jul 2016 10:14:01 -0400 |
| Subject: ext4: fix deadlock during page writeback |
| |
| From: Jan Kara <jack@suse.cz> |
| |
| commit 646caa9c8e196880b41cd3e3d33a2ebc752bdb85 upstream. |
| |
| Commit 06bd3c36a733 (ext4: fix data exposure after a crash) uncovered a |
| deadlock in ext4_writepages() which was previously much harder to hit. |
| After this commit xfstest generic/130 reproduces the deadlock on small |
| filesystems. |
| |
| The problem happens when ext4_do_update_inode() sets LARGE_FILE feature |
| and marks current inode handle as synchronous. That subsequently results |
| in ext4_journal_stop() called from ext4_writepages() to block waiting for |
| transaction commit while still holding page locks, reference to io_end, |
| and some prepared bio in mpd structure each of which can possibly block |
| transaction commit from completing and thus results in deadlock. |
| |
| Fix the problem by releasing page locks, io_end reference, and |
| submitting prepared bio before calling ext4_journal_stop(). |
| |
| [ Changed to defer the call to ext4_journal_stop() only if the handle |
| is synchronous. --tytso ] |
| |
| Reported-and-tested-by: Eryu Guan <eguan@redhat.com> |
| Signed-off-by: Theodore Ts'o <tytso@mit.edu> |
| Signed-off-by: Jan Kara <jack@suse.cz> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| fs/ext4/inode.c | 29 ++++++++++++++++++++++++++--- |
| 1 file changed, 26 insertions(+), 3 deletions(-) |
| |
| --- a/fs/ext4/inode.c |
| +++ b/fs/ext4/inode.c |
| @@ -2741,13 +2741,36 @@ retry: |
| done = true; |
| } |
| } |
| - ext4_journal_stop(handle); |
| + /* |
| + * Caution: If the handle is synchronous, |
| + * ext4_journal_stop() can wait for transaction commit |
| + * to finish which may depend on writeback of pages to |
| + * complete or on page lock to be released. In that |
| + * case, we have to wait until after after we have |
| + * submitted all the IO, released page locks we hold, |
| + * and dropped io_end reference (for extent conversion |
| + * to be able to complete) before stopping the handle. |
| + */ |
| + if (!ext4_handle_valid(handle) || handle->h_sync == 0) { |
| + ext4_journal_stop(handle); |
| + handle = NULL; |
| + } |
| /* Submit prepared bio */ |
| ext4_io_submit(&mpd.io_submit); |
| /* Unlock pages we didn't use */ |
| mpage_release_unused_pages(&mpd, give_up_on_write); |
| - /* Drop our io_end reference we got from init */ |
| - ext4_put_io_end(mpd.io_submit.io_end); |
| + /* |
| + * Drop our io_end reference we got from init. We have |
| + * to be careful and use deferred io_end finishing if |
| + * we are still holding the transaction as we can |
| + * release the last reference to io_end which may end |
| + * up doing unwritten extent conversion. |
| + */ |
| + if (handle) { |
| + ext4_put_io_end_defer(mpd.io_submit.io_end); |
| + ext4_journal_stop(handle); |
| + } else |
| + ext4_put_io_end(mpd.io_submit.io_end); |
| |
| if (ret == -ENOSPC && sbi->s_journal) { |
| /* |
