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: Hannes Reinecke <hare@suse.de>
Cc: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 2 insertions, 6 deletions

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index bdf26f5bd326..5adede17ddf6 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -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 @@ again:
 	}
 
 	if ((pgpath && m->queue_io) || (!pgpath && m->queue_if_no_path))
-		r = -EAGAIN;
+		r = -ENOTCONN;
 	else if (!bdev)
 		r = -EIO;
 
@@ -1591,11 +1590,8 @@ again:
 	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);
 }