From: Ming Lei <ming.lei@redhat.com>
Date: Tue, 27 Aug 2019 19:01:46 +0800
Subject: [PATCH] blk-mq: don't hold q->sysfs_lock in blk_mq_map_swqueue
References: bsc#1156419,jsc#SLE-8281
Git-commit: c6ba933358f0d7a6a042b894dba20cc70396a6d3
Patch-mainline: v5.4-rc1

blk_mq_map_swqueue() is called from blk_mq_init_allocated_queue()
and blk_mq_update_nr_hw_queues(). For the former caller, the kobject
isn't exposed to userspace yet. For the latter caller, hctx sysfs entries
and debugfs are un-registered before updating nr_hw_queues.

On the other hand, commit 2f8f1336a48b ("blk-mq: always free hctx after
request queue is freed") moves freeing hctx into queue's release
handler, so there won't be race with queue release path too.

So don't hold q->sysfs_lock in blk_mq_map_swqueue().

Cc: Christoph Hellwig <hch@infradead.org>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Mike Snitzer <snitzer@redhat.com>
Cc: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Hannes Reinecke <hare@suse.de>
---
 block/blk-mq.c | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 3c57ff633613..4b97a10755fe 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2456,11 +2456,6 @@ static void blk_mq_map_swqueue(struct request_queue *q)
 	struct blk_mq_ctx *ctx;
 	struct blk_mq_tag_set *set = q->tag_set;
 
-	/*
-	 * Avoid others reading imcomplete hctx->cpumask through sysfs
-	 */
-	mutex_lock(&q->sysfs_lock);
-
 	queue_for_each_hw_ctx(q, hctx, i) {
 		cpumask_clear(hctx->cpumask);
 		hctx->nr_ctx = 0;
@@ -2521,8 +2516,6 @@ static void blk_mq_map_swqueue(struct request_queue *q)
 					HCTX_TYPE_DEFAULT, i);
 	}
 
-	mutex_unlock(&q->sysfs_lock);
-
 	queue_for_each_hw_ctx(q, hctx, i) {
 		/*
 		 * If no software queues are mapped to this hardware queue,
-- 
2.16.4