tree 1240891ff1b9bfe1ba679ab5fef4655505602988
parent 8910c33882536ba00efc0768748e0846b40addcc
author Chris Mason <clm@fb.com> 1477590140 -0700
committer Greg Kroah-Hartman <gregkh@linuxfoundation.org> 1478792193 +0100

btrfs: fix races on root_log_ctx lists

commit 570dd45042a7c8a7aba1ee029c5dd0f5ccf41b9b upstream.

btrfs_remove_all_log_ctxs takes a shortcut where it avoids walking the
list because it knows all of the waiters are patiently waiting for the
commit to finish.

But, there's a small race where btrfs_sync_log can remove itself from
the list if it finds a log commit is already done.  Also, it uses
list_del_init() to remove itself from the list, but there's no way to
know if btrfs_remove_all_log_ctxs has already run, so we don't know for
sure if it is safe to call list_del_init().

This gets rid of all the shortcuts for btrfs_remove_all_log_ctxs(), and
just calls it with the proper locking.

This is part two of the corruption fixed by cbd60aa7cd1.  I should have
done this in the first place, but convinced myself the optimizations were
safe.  A 12 hour run of dbench 2048 will eventually trigger a list debug
WARN_ON for the list_del_init() in btrfs_sync_log().

Fixes: d1433debe7f4346cf9fc0dafc71c3137d2a97bc4
Reported-by: Dave Jones <davej@codemonkey.org.uk>
Signed-off-by: Chris Mason <clm@fb.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>