From nobody Fri Oct 3 03:21:29 2025 Received: from dggsgout12.his.huawei.com (dggsgout12.his.huawei.com [45.249.212.56]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6AC5922A4F8; Mon, 8 Sep 2025 06:40:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.56 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757313658; cv=none; b=R2xOiHNYYEJ2MHXTtTNCzAEdCHsk/UHNZm0zOYPW9zMCT6vYH6DLJ0zDXynAHKFG4Kp2ju+5Yypqu0PM+7kKs7MLmKhVDbhowuKTSVXV8L6NQmpHbKcCqBUWpKw87Anri3NAPhdN8KZps9WEq9a12EOiAwLm86VZW5Xv0+V65kw= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757313658; c=relaxed/simple; bh=pOPhOP9wjX3l36DHcRZ7tDtU3eF5RQ7aF999x4fzShM=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=V/25n+FkGmrnFz56y1dqlnRKq0Qii31BpC+cob1i3Z4ejWGwYzprLnzblQZ/dZ1uwASKFoB8BTETwnu7Uu/IyyBhWJvfNzp6NDQBxLhWIb4HVKNY5JrDnyQjoCRIvfA/4b6tnXJ6EDav0uEUQ4Acw7JIlNhao5sclfFYm/mYvdc= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=huaweicloud.com; spf=pass smtp.mailfrom=huaweicloud.com; arc=none smtp.client-ip=45.249.212.56 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=huaweicloud.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huaweicloud.com Received: from mail.maildlp.com (unknown [172.19.93.142]) by dggsgout12.his.huawei.com (SkyGuard) with ESMTPS id 4cKxks3YsZzKHMxf; Mon, 8 Sep 2025 14:24:53 +0800 (CST) Received: from mail02.huawei.com (unknown [10.116.40.128]) by mail.maildlp.com (Postfix) with ESMTP id 91CFF1A0AD9; Mon, 8 Sep 2025 14:24:53 +0800 (CST) Received: from huaweicloud.com (unknown [10.175.104.67]) by APP4 (Coremail) with SMTP id gCh0CgD3QY6xdr5oCGEjBw--.62066S8; Mon, 08 Sep 2025 14:24:53 +0800 (CST) From: Yu Kuai To: nilay@linux.ibm.com, ming.lei@redhat.com, axboe@kernel.dk Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, yukuai3@huawei.com, yukuai1@huaweicloud.com, yi.zhang@huawei.com, yangerkun@huawei.com, johnny.chenyi@huawei.com Subject: [PATCH for-6.18/block 04/10] blk-mq: convert to serialize updating nr_requests with update_nr_hwq_lock Date: Mon, 8 Sep 2025 14:15:27 +0800 Message-Id: <20250908061533.3062917-5-yukuai1@huaweicloud.com> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20250908061533.3062917-1-yukuai1@huaweicloud.com> References: <20250908061533.3062917-1-yukuai1@huaweicloud.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-CM-TRANSID: gCh0CgD3QY6xdr5oCGEjBw--.62066S8 X-Coremail-Antispam: 1UD129KBjvJXoW7Cw1DKrWfuw13CF47tr1xuFg_yoW8ZrWxpF W3Ca9Fkw1vq3W8X34UAw17WwnrJw4Igr17GrWxtF1ayFnrt3Z7ZF18KFy8WF4IkrZ3AFsI vFWkXFZ5ZFyDZF7anT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUm214x267AKxVWrJVCq3wAFc2x0x2IEx4CE42xK8VAvwI8IcIk0 rVWrJVCq3wAFIxvE14AKwVWUJVWUGwA2048vs2IY020E87I2jVAFwI0_JF0E3s1l82xGYI kIc2x26xkF7I0E14v26ryj6s0DM28lY4IEw2IIxxk0rwA2F7IY1VAKz4vEj48ve4kI8wA2 z4x0Y4vE2Ix0cI8IcVAFwI0_tr0E3s1l84ACjcxK6xIIjxv20xvEc7CjxVAFwI0_Gr1j6F 4UJwA2z4x0Y4vEx4A2jsIE14v26rxl6s0DM28EF7xvwVC2z280aVCY1x0267AKxVW0oVCq 3wAS0I0E0xvYzxvE52x082IY62kv0487Mc02F40EFcxC0VAKzVAqx4xG6I80ewAv7VC0I7 IYx2IY67AKxVWUJVWUGwAv7VC2z280aVAFwI0_Jr0_Gr1lOx8S6xCaFVCjc4AY6r1j6r4U M4x0Y48IcxkI7VAKI48JM4x0x7Aq67IIx4CEVc8vx2IErcIFxwACI402YVCY1x02628vn2 kIc2xKxwCY1x0262kKe7AKxVWUtVW8ZwCF04k20xvY0x0EwIxGrwCFx2IqxVCFs4IE7xkE bVWUJVW8JwC20s026c02F40E14v26r1j6r18MI8I3I0E7480Y4vE14v26r106r1rMI8E67 AF67kF1VAFwI0_Jw0_GFylIxkGc2Ij64vIr41lIxAIcVC0I7IYx2IY67AKxVWUJVWUCwCI 42IY6xIIjxv20xvEc7CjxVAFwI0_Gr0_Cr1lIxAIcVCF04k26cxKx2IYs7xG6r1j6r1xMI IF0xvEx4A2jsIE14v26r1j6r4UMIIF0xvEx4A2jsIEc7CjxVAFwI0_Gr0_Gr1UYxBIdaVF xhVjvjDU0xZFpf9x0JUQFxUUUUUU= X-CM-SenderInfo: 51xn3trlr6x35dzhxuhorxvhhfrp/ Content-Type: text/plain; charset="utf-8" From: Yu Kuai request_queue->nr_requests can be changed by: a) switching elevator by update nr_hw_queues b) switching elevator by elevator sysfs attribute c) configue queue sysfs attribute nr_requests Current lock order is: 1) update_nr_hwq_lock, case a,b 2) freeze_queue 3) elevator_lock, cas a,b,c And update nr_requests is seriablized by elevator_lock() already, however, in the case c), we'll have to allocate new sched_tags if nr_requests grow, and do this with elevator_lock held and queue freezed has the risk of deadlock. Hence use update_nr_hwq_lock instead, make it possible to allocate memory if tags grow, meanwhile also prevent nr_requests to be changed concurrently. Signed-off-by: Yu Kuai Reviewed-by: Nilay Shroff --- block/blk-sysfs.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index f99519f7a820..7ea15bf68b4b 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -68,13 +68,14 @@ queue_requests_store(struct gendisk *disk, const char *= page, size_t count) int ret, err; unsigned int memflags; struct request_queue *q =3D disk->queue; + struct blk_mq_tag_set *set =3D q->tag_set; =20 ret =3D queue_var_store(&nr, page, count); if (ret < 0) return ret; =20 - memflags =3D blk_mq_freeze_queue(q); - mutex_lock(&q->elevator_lock); + /* serialize updating nr_requests with switching elevator */ + down_write(&set->update_nr_hwq_lock); =20 if (nr =3D=3D q->nr_requests) goto unlock; @@ -89,13 +90,18 @@ queue_requests_store(struct gendisk *disk, const char *= page, size_t count) goto unlock; } =20 + memflags =3D blk_mq_freeze_queue(q); + mutex_lock(&q->elevator_lock); + err =3D blk_mq_update_nr_requests(disk->queue, nr); if (err) ret =3D err; =20 -unlock: mutex_unlock(&q->elevator_lock); blk_mq_unfreeze_queue(q, memflags); + +unlock: + up_write(&set->update_nr_hwq_lock); return ret; } =20 --=20 2.39.2