1 files changed, 21 insertions, 5 deletions

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 7ad7c11fe01d..4bf850e8d6b5 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1870,7 +1870,7 @@ static void blk_mq_init_cpu_queues(struct request_queue *q,
 static void blk_mq_map_swqueue(struct request_queue *q,
                                const struct cpumask *online_mask)
 {
-        unsigned int i;
+        unsigned int i, hctx_idx;
         struct blk_mq_hw_ctx *hctx;
         struct blk_mq_ctx *ctx;
         struct blk_mq_tag_set *set = q->tag_set;
@@ -1893,6 +1893,21 @@ static void blk_mq_map_swqueue(struct request_queue *q,
                 if (!cpumask_test_cpu(i, online_mask))
                         continue;
 
+                hctx_idx = q->mq_map[i];
+                /* unmapped hw queue can be remapped after CPU topo changed */
+                if (!set->tags[hctx_idx]) {
+                        set->tags[hctx_idx] = blk_mq_init_rq_map(set, hctx_idx);
+
+                        /*
+                         * If tags initialization fail for some hctx,
+                         * that hctx won't be brought online.  In this
+                         * case, remap the current ctx to hctx[0] which
+                         * is guaranteed to always have tags allocated
+                         */
+                        if (!set->tags[hctx_idx])
+                                q->mq_map[i] = 0;
+                }
+
                 ctx = per_cpu_ptr(q->queue_ctx, i);
                 hctx = blk_mq_map_queue(q, i);
 
@@ -1909,7 +1924,11 @@ static void blk_mq_map_swqueue(struct request_queue *q,
                  * disable it and free the request entries.
                  */
                 if (!hctx->nr_ctx) {
-                        if (set->tags[i]) {
+                        /* Never unmap queue 0.  We need it as a
+                         * fallback in case of a new remap fails
+                         * allocation
+                         */
+                        if (i && set->tags[i]) {
                                 blk_mq_free_rq_map(set, set->tags[i], i);
                                 set->tags[i] = NULL;
                         }
@@ -1917,9 +1936,6 @@ static void blk_mq_map_swqueue(struct request_queue *q,
                         continue;
                 }
 
-                /* unmapped hw queue can be remapped after CPU topo changed */
-                if (!set->tags[i])
-                        set->tags[i] = blk_mq_init_rq_map(set, i);
                 hctx->tags = set->tags[i];
                 WARN_ON(!hctx->tags);