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Commit 6c182cd8 authored by Hannes Reinecke's avatar Hannes Reinecke Committed by Alasdair G Kergon
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dm mpath: fix ioctl deadlock when no paths 



When multipath needs to retry an ioctl the reference to the
current live table needs to be dropped. Otherwise a deadlock
occurs when all paths are down:
- dm_blk_ioctl takes a reference to the current table
  and spins in multipath_ioctl().
- A new table is being loaded, but upon resume the process
  hangs in dm_table_destroy() waiting for references to
  drop to zero.

With this patch the reference to the old table is dropped
prior to retry, thereby avoiding the deadlock.

Signed-off-by: default avatarHannes Reinecke <hare@suse.de>
Cc: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: default avatarAlasdair G Kergon <agk@redhat.com>
parent 8bb495e3

drivers/md/dm-mpath.c

+2 −6
Original line number Diff line number Diff line
@@ -1561,7 +1561,6 @@ static int multipath_ioctl(struct dm_target *ti, unsigned int cmd, 
	unsigned long flags;

	int r;



again:

	bdev = NULL;

	mode = 0;

	r = 0;
@@ -1579,7 +1578,7 @@ static int multipath_ioctl(struct dm_target *ti, unsigned int cmd, 
	}



	if ((pgpath && m->queue_io) || (!pgpath && m->queue_if_no_path))

		r = -EAGAIN;

		r = -ENOTCONN;

	else if (!bdev)

		r = -EIO;
@@ -1591,11 +1590,8 @@ static int multipath_ioctl(struct dm_target *ti, unsigned int cmd, 
	if (!r && ti->len != i_size_read(bdev->bd_inode) >> SECTOR_SHIFT)

		r = scsi_verify_blk_ioctl(NULL, cmd);



	if (r == -EAGAIN && !fatal_signal_pending(current)) {

	if (r == -ENOTCONN && !fatal_signal_pending(current))

		queue_work(kmultipathd, &m->process_queued_ios);

		msleep(10);

		goto again;

	}



	return r ? : __blkdev_driver_ioctl(bdev, mode, cmd, arg);

}

drivers/md/dm.c

+8 −1
Original line number Diff line number Diff line
@@ -386,10 +386,12 @@ static int dm_blk_ioctl(struct block_device *bdev, fmode_t mode, 
			unsigned int cmd, unsigned long arg)

{

	struct mapped_device *md = bdev->bd_disk->private_data;

	struct dm_table *map = dm_get_live_table(md);

	struct dm_table *map;

	struct dm_target *tgt;

	int r = -ENOTTY;



retry:

	map = dm_get_live_table(md);

	if (!map || !dm_table_get_size(map))

		goto out;
@@ -410,6 +412,11 @@ static int dm_blk_ioctl(struct block_device *bdev, fmode_t mode, 
out:

	dm_table_put(map);



	if (r == -ENOTCONN) {

		msleep(10);

		goto retry;

	}



	return r;

}