Revert "blk-mq: remove code for dealing with remapping queue"

This reverts commit 37c7c6c76d431dd7ef9c29d95f6052bd425f004c.

Turns out some drivers(most are FC drivers) may not use managed
IRQ affinity, and has their customized .map_queues meantime, so
still keep this code for avoiding regression.

Reported-by: Laurence Oberman <loberman@redhat.com>
Tested-by: Laurence Oberman <loberman@redhat.com>
Tested-by: Christian Borntraeger <borntraeger@de.ibm.com>
Tested-by: Stefan Haberland <sth@linux.vnet.ibm.com>
Cc: Ewan Milne <emilne@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 31 insertions, 3 deletions

diff --git a/block/blk-mq.c b/block/blk-mq.c
index e4aa36817367..c3621453ad87 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2336,7 +2336,7 @@ static void blk_mq_free_map_and_requests(struct blk_mq_tag_set *set,
 
 static void blk_mq_map_swqueue(struct request_queue *q)
 {
-        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;
@@ -2353,8 +2353,23 @@ static void blk_mq_map_swqueue(struct request_queue *q)
 
         /*
          * Map software to hardware queues.
+         *
+         * If the cpu isn't present, the cpu is mapped to first hctx.
          */
         for_each_possible_cpu(i) {
+                hctx_idx = q->mq_map[i];
+                /* unmapped hw queue can be remapped after CPU topo changed */
+                if (!set->tags[hctx_idx] &&
+                    !__blk_mq_alloc_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
+                         */
+                        q->mq_map[i] = 0;
+                }
+
                 ctx = per_cpu_ptr(q->queue_ctx, i);
                 hctx = blk_mq_map_queue(q, i);
 
@@ -2366,8 +2381,21 @@ static void blk_mq_map_swqueue(struct request_queue *q)
         mutex_unlock(&q->sysfs_lock);
 
         queue_for_each_hw_ctx(q, hctx, i) {
-                /* every hctx should get mapped by at least one CPU */
-                WARN_ON(!hctx->nr_ctx);
+                /*
+                 * If no software queues are mapped to this hardware queue,
+                 * disable it and free the request entries.
+                 */
+                if (!hctx->nr_ctx) {
+                        /* 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_map_and_requests(set, i);
+
+                        hctx->tags = NULL;
+                        continue;
+                }
 
                 hctx->tags = set->tags[i];
                 WARN_ON(!hctx->tags);