[PATCH 2/2] block: avoid to reuse `hctx` not removed from cpuhp callback list

[Ming Lei <ming.lei@redhat.com>]

If the 'hctx' isn't removed from cpuhp callback list, we can't reuse it,
otherwise use-after-free may be triggered.

Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202412172217.b906db7c-lkp@intel.com
Tested-by: kernel test robot <oliver.sang@intel.com>
Fixes: 22465bbac53c ("blk-mq: move cpuhp callback registering out of q->sysfs_lock")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 block/blk-mq.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 92e8ddf34575..8ac19d4ae3c0 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -4412,6 +4412,15 @@ struct gendisk *blk_mq_alloc_disk_for_queue(struct request_queue *q,
 }
 EXPORT_SYMBOL(blk_mq_alloc_disk_for_queue);
 
+/*
+ * Only hctx removed from cpuhp list can be reused
+ */
+static bool blk_mq_hctx_is_reusable(struct blk_mq_hw_ctx *hctx)
+{
+	return hlist_unhashed(&hctx->cpuhp_online) &&
+		hlist_unhashed(&hctx->cpuhp_dead);
+}
+
 static struct blk_mq_hw_ctx *blk_mq_alloc_and_init_hctx(
 		struct blk_mq_tag_set *set, struct request_queue *q,
 		int hctx_idx, int node)
@@ -4421,7 +4430,7 @@ static struct blk_mq_hw_ctx *blk_mq_alloc_and_init_hctx(
 	/* reuse dead hctx first */
 	spin_lock(&q->unused_hctx_lock);
 	list_for_each_entry(tmp, &q->unused_hctx_list, hctx_list) {
-		if (tmp->numa_node == node) {
+		if (tmp->numa_node == node && blk_mq_hctx_is_reusable(tmp)) {
 			hctx = tmp;
 			break;
 		}
-- 
2.47.0