blk-mq: prealloc tags when increase tagset nr_hw_queues

Just like blk_mq_alloc_tag_set(), it's better to prepare all tags before
using to map to queue ctxs in blk_mq_map_swqueue(), which now have to
consider empty set->tags[].

The good point is that we can fallback easily if increasing nr_hw_queues
fail, instead of just mapping to hctx[0] when fail in blk_mq_map_swqueue().

And the fallback path already has tags free & clean handling, so all
is good.

Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20230821095602.70742-3-chengming.zhou@linux.dev
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 22397ba..8440015 100644 (file)
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -4397,6 +4397,16 @@ static int blk_mq_realloc_tag_set_tags(struct blk_mq_tag_set *set,
                       sizeof(*set->tags));
        kfree(set->tags);
        set->tags = new_tags;
+
+       for (i = set->nr_hw_queues; i < new_nr_hw_queues; i++) {
+               if (!__blk_mq_alloc_map_and_rqs(set, i)) {
+                       while (--i >= set->nr_hw_queues)
+                               __blk_mq_free_map_and_rqs(set, i);
+                       return -ENOMEM;
+               }
+               cond_resched();
+       }
+
 done:
        set->nr_hw_queues = new_nr_hw_queues;
        return 0;