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Commit b7934ba4 authored by Jens Axboe's avatar Jens Axboe
Browse files

dm: fix inflight IO check 



After switching to percpu inflight counters, the inflight check
is totally buggy. It's perfectly valid for some counters to be
non-zero while having a total inflight IO count of 0, that's how
these kinds of counters work (inc on one CPU, dec on another).
Fix the md_in_flight() check to sum all counters before returning
a false positive, potentially.

While at it, remove the inflight read for IO completion. We don't
need it, just wake anyone that's waiting for the IO count to drop
to zero. The caller needs to re-check that value anyway when woken,
which it does.

Fixes: 6f757231 ("dm: remove the pending IO accounting")
Acked-by: default avatarMike Snitzer <snitzer@redhat.com>
Reported-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 4ba09f69

drivers/md/dm.c

+6 −8
Original line number Diff line number Diff line
@@ -650,14 +650,14 @@ static bool md_in_flight(struct mapped_device *md) 
{

	int cpu;

	struct hd_struct *part = &dm_disk(md)->part0;

	long sum = 0;



	for_each_possible_cpu(cpu) {

		if (part_stat_local_read_cpu(part, in_flight[0], cpu) ||

		    part_stat_local_read_cpu(part, in_flight[1], cpu))

			return true;

		sum += part_stat_local_read_cpu(part, in_flight[0], cpu);

		sum += part_stat_local_read_cpu(part, in_flight[1], cpu);

	}



	return false;

	return sum != 0;

}



static void start_io_acct(struct dm_io *io)
@@ -691,11 +691,9 @@ static void end_io_acct(struct dm_io *io) 
				    true, duration, &io->stats_aux);



	/* nudge anyone waiting on suspend queue */

	if (unlikely(waitqueue_active(&md->wait))) {

		if (!md_in_flight(md))

	if (unlikely(waitqueue_active(&md->wait)))

		wake_up(&md->wait);

}

}



/*

 * Add the bio to the list of deferred io.