dm: detect lost queue

Detect and report buggy drivers that destroy their request_queue.

Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Cc: Stefan Raspl <raspl@linux.vnet.ibm.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 23 insertions, 3 deletions

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 5dd32b8a57ac..a740a6950f59 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -482,6 +482,13 @@ void dm_set_device_limits(struct dm_target *ti, struct block_device *bdev)
 {
         struct request_queue *q = bdev_get_queue(bdev);
         struct io_restrictions *rs = &ti->limits;
+        char b[BDEVNAME_SIZE];
+
+        if (unlikely(!q)) {
+                DMWARN("%s: Cannot set limits for nonexistent device %s",
+                       dm_device_name(ti->table->md), bdevname(bdev, b));
+                return;
+        }
 
         /*
          * Combine the device limits low.
@@ -950,7 +957,14 @@ int dm_table_any_congested(struct dm_table *t, int bdi_bits)
 
         list_for_each_entry(dd, devices, list) {
                 struct request_queue *q = bdev_get_queue(dd->dm_dev.bdev);
-                r |= bdi_congested(&q->backing_dev_info, bdi_bits);
+                char b[BDEVNAME_SIZE];
+
+                if (likely(q))
+                        r |= bdi_congested(&q->backing_dev_info, bdi_bits);
+                else
+                        DMWARN_LIMIT("%s: any_congested: nonexistent device %s",
+                                     dm_device_name(t->md),
+                                     bdevname(dd->dm_dev.bdev, b));
         }
 
         return r;
@@ -963,8 +977,14 @@ void dm_table_unplug_all(struct dm_table *t)
 
         list_for_each_entry(dd, devices, list) {
                 struct request_queue *q = bdev_get_queue(dd->dm_dev.bdev);
-
-                blk_unplug(q);
+                char b[BDEVNAME_SIZE];
+
+                if (likely(q))
+                        blk_unplug(q);
+                else
+                        DMWARN_LIMIT("%s: Cannot unplug nonexistent device %s",
+                                     dm_device_name(t->md),
+                                     bdevname(dd->dm_dev.bdev, b));
         }
 }