Oleg Nesterov 89f39af129 fs/super.c: fix race between freeze_super() and thaw_super()
Change thaw_super() to check frozen != SB_FREEZE_COMPLETE rather than
frozen == SB_UNFROZEN, otherwise it can race with freeze_super() which
drops sb->s_umount after SB_FREEZE_WRITE to preserve the lock ordering.

In this case thaw_super() will wrongly call s_op->unfreeze_fs() before
it was actually frozen, and call sb_freeze_unlock() which leads to the
unbalanced percpu_up_write(). Unfortunately lockdep can't detect this,
so this triggers misc BUG_ON()'s in kernel/rcu/sync.c.

Reported-and-tested-by: Nikolay Borisov <kernel@kyup.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2016-10-14 20:00:34 -04:00
..
2016-10-07 15:15:33 -07:00
2016-10-11 10:49:44 -07:00
2016-09-27 21:20:53 -04:00
2016-06-07 22:07:09 -04:00
2016-09-27 18:47:38 -04:00
2016-06-21 09:23:11 +10:00
2016-07-26 16:19:19 -07:00