Commit 8a57dfc6 authored Nov 13, 2008 by Chandra Seetharaman Committed by Alasdair G Kergon Nov 13, 2008

dm: avoid destroying table in dm_any_congested



dm_any_congested() just checks for the DMF_BLOCK_IO and has no
code to make sure that suspend waits for dm_any_congested() to
complete.  This patch adds such a check.

Without it, a race can occur with dm_table_put() attempting to
destroying the table in the wrong thread, the one running
dm_any_congested() which is meant to be quick and return
immediately.

Two examples of problems:
1. Sleeping functions called from congested code, the caller
   of which holds a spin lock.
2. An ABBA deadlock between pdflush and multipathd. The two locks
   in contention are inode lock and kernel lock.

Signed-off-by: Chandra Seetharaman <sekharan@us.ibm.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

parent d221d2e7

drivers/md/dm.c

+16 −8

Original line number	Diff line number	Diff line
		@@ -937,16 +937,24 @@ static void dm_unplug_all(struct request_queue *q)

		static int dm_any_congested(void *congested_data, int bdi_bits)
		{
		int r;
		struct mapped_device md = (struct mapped_device ) congested_data;
		struct dm_table *map = dm_get_table(md);
		int r = bdi_bits;
		struct mapped_device *md = congested_data;
		struct dm_table *map;

		if (!map \|\| test_bit(DMF_BLOCK_IO, &md->flags))
		r = bdi_bits;
		else
		r = dm_table_any_congested(map, bdi_bits);
		atomic_inc(&md->pending);

		if (!test_bit(DMF_BLOCK_IO, &md->flags)) {
		map = dm_get_table(md);
		if (map) {
		r = dm_table_any_congested(map, bdi_bits);
		dm_table_put(map);
		}
		}

		if (!atomic_dec_return(&md->pending))
		/* nudge anyone waiting on suspend queue */
		wake_up(&md->wait);

		return r;
		}