Commit c322ee93 authored Aug 24, 2020 by Mike Snitzer

dm mpath: fix racey management of PG initialization



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: Ben Marzinski <bmarzins@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

parent f9e040ef

drivers/md/dm-mpath.c

+15 −7

Original line number	Diff line number	Diff line
		@@ -1287,17 +1287,25 @@ 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);

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