blk-mq: add helper for checking if one CPU is mapped to specified hctx

Commit a46c270 ("blk-mq: don't schedule block kworker on isolated CPUs")
rules out isolated CPUs from hctx->cpumask, and hctx->cpumask should only be
used for scheduling kworker.

Add helper blk_mq_cpu_mapped_to_hctx() and apply it into cpuhp handlers.

This patch avoids to forget clearing INACTIVE of hctx state in case that one
isolated CPU becomes online, and fixes hang issue when allocating request
from this hctx's tags.

Cc: Raju Cheerla <rcheerla@redhat.com>
Fixes: a46c270 ("blk-mq: don't schedule block kworker on isolated CPUs")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20240517020514.149771-1-ming.lei@redhat.com
Tested-by: Raju Cheerla <rcheerla@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-mq.c

@@ -3545,12 +3545,28 @@ static int blk_mq_hctx_notify_offline(unsigned int cpu, struct hlist_node *node)
 	return 0;
 }
 
+/*
+ * Check if one CPU is mapped to the specified hctx
+ *
+ * Isolated CPUs have been ruled out from hctx->cpumask, which is supposed
+ * to be used for scheduling kworker only. For other usage, please call this
+ * helper for checking if one CPU belongs to the specified hctx
+ */
+static bool blk_mq_cpu_mapped_to_hctx(unsigned int cpu,
+		const struct blk_mq_hw_ctx *hctx)
+{
+	struct blk_mq_hw_ctx *mapped_hctx = blk_mq_map_queue_type(hctx->queue,
+			hctx->type, cpu);
+
+	return mapped_hctx == hctx;
+}
+
 static int blk_mq_hctx_notify_online(unsigned int cpu, struct hlist_node *node)
 {
 	struct blk_mq_hw_ctx *hctx = hlist_entry_safe(node,
 			struct blk_mq_hw_ctx, cpuhp_online);
 
-	if (cpumask_test_cpu(cpu, hctx->cpumask))
+	if (blk_mq_cpu_mapped_to_hctx(cpu, hctx))
 		clear_bit(BLK_MQ_S_INACTIVE, &hctx->state);
 	return 0;
 }
@@ -3568,7 +3584,7 @@ static int blk_mq_hctx_notify_dead(unsigned int cpu, struct hlist_node *node)
 	enum hctx_type type;
 
 	hctx = hlist_entry_safe(node, struct blk_mq_hw_ctx, cpuhp_dead);
-	if (!cpumask_test_cpu(cpu, hctx->cpumask))
+	if (!blk_mq_cpu_mapped_to_hctx(cpu, hctx))
 		return 0;
 
 	ctx = __blk_mq_get_ctx(hctx->queue, cpu);