6.6-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ming Lei <redacted>

commit c25c0c9035bb8b28c844dfddeda7b8bdbcfcae95 upstream.

Commit 7b815817aa58 ("blk-mq: add helper for checking if one CPU is mapped to specified hctx")
needs to check queue mapping via tag set in hctx's cpuhp handler.

However, q->tag_set may not be setup yet when the cpuhp handler is
enabled, then kernel oops is triggered.

Fix the issue by setup queue tag_set before initializing hctx.

Cc: stable@vger.kernel.org
Reported-and-tested-by: Rick Koch <redacted>
Closes: https://lore.kernel.org/linux-block/CANa58eeNDozLaBHKPLxSAhEy__FPfJT_F71W=sEQw49UCrC9PQ@mail.gmail.com (local)
Fixes: 7b815817aa58 ("blk-mq: add helper for checking if one CPU is mapped to specified hctx")
Signed-off-by: Ming Lei <redacted>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: John Garry <john.g.garry@oracle.com>
Link: https://lore.kernel.org/r/20241014005115.2699642-1-ming.lei@redhat.com (local)
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 block/blk-mq.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/block/blk-mq.c
+++ b/block/blk-mq.c

@@ -4453,6 +4453,12 @@ int blk_mq_init_allocated_queue(struct b
 	/* mark the queue as mq asap */
 	q->mq_ops = set->ops;
 
+	/*
+	 * ->tag_set has to be setup before initialize hctx, which cpuphp
+	 * handler needs it for checking queue mapping
+	 */
+	q->tag_set = set;
+
 	if (blk_mq_alloc_ctxs(q))
 		goto err_exit;
 

@@ -4471,8 +4477,6 @@ int blk_mq_init_allocated_queue(struct b
 	INIT_WORK(&q->timeout_work, blk_mq_timeout_work);
 	blk_queue_rq_timeout(q, set->timeout ? set->timeout : 30 * HZ);
 
-	q->tag_set = set;
-
 	q->queue_flags |= QUEUE_FLAG_MQ_DEFAULT;
 	blk_mq_update_poll_flag(q);