[PATCH v2] blk-mq: remap queues when adding/removing hardware queues

[Omar Sandoval]

From: Omar Sandoval <osan...@fb.com>

blk_mq_update_nr_hw_queues() used to remap hardware queues, which is the
behavior that drivers expect. However, commit 4e68a011428a changed
blk_mq_queue_reinit() to not remap queues for the case of CPU
hotplugging, inadvertently making blk_mq_update_nr_hw_queues() not remap
queues as well. This breaks, for example, NBD's multi-connection mode,
leaving the added hardware queues unused. Fix it by making
blk_mq_update_nr_hw_queues() explicitly remap the queues.

Fixes: 4e68a011428a ("blk-mq: don't redistribute hardware queues on a CPU 
hotplug event")
Signed-off-by: Omar Sandoval <osan...@fb.com>
---
 block/blk-mq.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 061fc2cc88d3..70fa2b0d385a 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2478,6 +2478,14 @@ static int blk_mq_alloc_rq_maps(struct blk_mq_tag_set 
*set)
        return 0;
 }
 
+static int blk_mq_update_queue_map(struct blk_mq_tag_set *set)
+{
+       if (set->ops->map_queues)
+               return set->ops->map_queues(set);
+       else
+               return blk_mq_map_queues(set);
+}
+
 /*
  * Alloc a tag set to be associated with one or more request queues.
  * May fail with EINVAL for various error conditions. May adjust the
@@ -2532,10 +2540,7 @@ int blk_mq_alloc_tag_set(struct blk_mq_tag_set *set)
        if (!set->mq_map)
                goto out_free_tags;
 
-       if (set->ops->map_queues)
-               ret = set->ops->map_queues(set);
-       else
-               ret = blk_mq_map_queues(set);
+       ret = blk_mq_update_queue_map(set);
        if (ret)
                goto out_free_mq_map;
 
@@ -2627,6 +2632,7 @@ void blk_mq_update_nr_hw_queues(struct blk_mq_tag_set 
*set, int nr_hw_queues)
                blk_mq_freeze_queue(q);
 
        set->nr_hw_queues = nr_hw_queues;
+       blk_mq_update_queue_map(set);
        list_for_each_entry(q, &set->tag_list, tag_set_list) {
                blk_mq_realloc_hw_ctxs(set, q);
                blk_mq_queue_reinit(q, cpu_online_mask);
@@ -2634,6 +2640,7 @@ void blk_mq_update_nr_hw_queues(struct blk_mq_tag_set 
*set, int nr_hw_queues)
 
        list_for_each_entry(q, &set->tag_list, tag_set_list)
                blk_mq_unfreeze_queue(q);
+
 }
 EXPORT_SYMBOL_GPL(blk_mq_update_nr_hw_queues);
 
-- 
2.12.1