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>

2 files changed, 10 insertions, 7 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);
 }
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index d5370a94b2c1..33f20103d8d5 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -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;
 }