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>

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index bdf26f5..5adede1 100644 (file)
--- 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 d5370a9..33f2010 100644 (file)
--- 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;
 }