blk-mq: avoid setting hctx->tags->cpumask before allocation

When unmapped hw queue is remapped after CPU topology is changed,
hctx->tags->cpumask has to be set after hctx->tags is setup in
blk_mq_map_swqueue(), otherwise it causes null pointer dereference.

Fixes: f26cdc8536 ("blk-mq: Shared tag enhancements")
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Keith Busch <keith.busch@intel.com>
Cc: Ming Lei <tom.leiming@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 8 insertions, 1 deletions

diff --git a/block/blk-mq.c b/block/blk-mq.c
index f2d67b4047a0..2fd7283ec62b 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1811,7 +1811,6 @@ static void blk_mq_map_swqueue(struct request_queue *q)
 
                 hctx = q->mq_ops->map_queue(q, i);
                 cpumask_set_cpu(i, hctx->cpumask);
-                cpumask_set_cpu(i, hctx->tags->cpumask);
                 ctx->index_hw = hctx->nr_ctx;
                 hctx->ctxs[hctx->nr_ctx++] = ctx;
         }
@@ -1851,6 +1850,14 @@ static void blk_mq_map_swqueue(struct request_queue *q)
                 hctx->next_cpu = cpumask_first(hctx->cpumask);
                 hctx->next_cpu_batch = BLK_MQ_CPU_WORK_BATCH;
         }
+
+        queue_for_each_ctx(q, ctx, i) {
+                if (!cpu_online(i))
+                        continue;
+
+                hctx = q->mq_ops->map_queue(q, i);
+                cpumask_set_cpu(i, hctx->tags->cpumask);
+        }
 }
 
 static void blk_mq_update_tag_set_depth(struct blk_mq_tag_set *set)