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Commit b30f628b authored by Mike Snitzer's avatar Mike Snitzer Committed by Greg Kroah-Hartman
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dm mpath: fix racey management of PG initialization 



commit c322ee9320eaa4013ca3620b1130992916b19b31 upstream.

Commit 935fcc56 ("dm mpath: only flush workqueue when needed")
changed flush_multipath_work() to avoid needless workqueue
flushing (of a multipath global workqueue). But that change didn't
realize the surrounding flush_multipath_work() code should also only
run if 'pg_init_in_progress' is set.

Fix this by only doing all of flush_multipath_work()'s PG init related
work if 'pg_init_in_progress' is set.

Otherwise multipath_wait_for_pg_init_completion() will run
unconditionally but the preceeding flush_workqueue(kmpath_handlerd)
may not. This could lead to deadlock (though only if kmpath_handlerd
never runs a corresponding work to decrement 'pg_init_in_progress').

It could also be, though highly unlikely, that the kmpath_handlerd
work that does PG init completes before 'pg_init_in_progress' is set,
and then an intervening DM table reload's multipath_postsuspend()
triggers flush_multipath_work().

Fixes: 935fcc56 ("dm mpath: only flush workqueue when needed")
Cc: stable@vger.kernel.org
Reported-by: default avatarBen Marzinski <bmarzins@redhat.com>
Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 226fb99e

drivers/md/dm-mpath.c

+15 −7
Original line number Diff line number Diff line
@@ -1190,17 +1190,25 @@ static void multipath_wait_for_pg_init_completion(struct multipath *m) 
static void flush_multipath_work(struct multipath *m)

{

	if (m->hw_handler_name) {

		set_bit(MPATHF_PG_INIT_DISABLED, &m->flags);

		smp_mb__after_atomic();

		unsigned long flags;



		if (!atomic_read(&m->pg_init_in_progress))

			goto skip;



		spin_lock_irqsave(&m->lock, flags);

		if (atomic_read(&m->pg_init_in_progress) &&

		    !test_and_set_bit(MPATHF_PG_INIT_DISABLED, &m->flags)) {

			spin_unlock_irqrestore(&m->lock, flags);



		if (atomic_read(&m->pg_init_in_progress))

			flush_workqueue(kmpath_handlerd);

			multipath_wait_for_pg_init_completion(m);



			spin_lock_irqsave(&m->lock, flags);

			clear_bit(MPATHF_PG_INIT_DISABLED, &m->flags);

		smp_mb__after_atomic();

		}



		spin_unlock_irqrestore(&m->lock, flags);

	}

skip:

	if (m->queue_mode == DM_TYPE_BIO_BASED)

		flush_work(&m->process_queued_bios);

	flush_work(&m->trigger_event);