diff options
| author | Jan Kara <jack@suse.cz> | 2016-07-04 10:14:01 -0400 |
|---|---|---|
| committer | Theodore Ts'o <tytso@mit.edu> | 2016-07-04 10:14:01 -0400 |
| commit | 646caa9c8e196880b41cd3e3d33a2ebc752bdb85 (patch) | |
| tree | 28d3c6dcf43b1ba8e8d1b5eff334b9c07b098db2 /fs/ext4 | |
| parent | fa96454069b85a7e5d10f38b7d95edcd5dc64b9a (diff) | |
ext4: fix deadlock during page writeback
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>
CC: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
Diffstat (limited to 'fs/ext4')
| -rw-r--r-- | fs/ext4/inode.c | 29 |
1 files changed, 26 insertions, 3 deletions
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index 44ee5d933b36..321a31cef59c 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -2754,13 +2754,36 @@ 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) { /* |