From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 618F2CFA466 for ; Mon, 24 Nov 2025 04:00:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=DdDKO8bUz7vs53nrnYdRyFnOzZ+W0EnIA6of8FyzT0A=; b=l7kjN+jIsRM0ymQMMU1BjvUqpI x4LzLwmp+KcCA9kpb637Fb9W/6ZrV+XifbZ6lmoArZOSN5ifBAj3F4sSa3mqjj/blrVG4qfjV+nDU hNw0whsiGQ3mTY9tkcDb6kmd1MsIu5BH7Px63oZ9rLSkWuYQxlifIKpEGUq0b7rpmHZ8kVJbi7LA/ eM7DvNOLB+zQAXmRI6Gy7w67Zk2j7z4cffOswS5M3RFLf4ltxbb3084bv1/Wv9ZmJCc6zZVYL3+Nz 4AOp8ADHNzH3C9PAMGF35W6Q4lvUV8u4OTpj9ru6qfiKMSnDe26hIXJNmi+d7glPc0cZ9fqP359SY f0+5yj/Q==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vNNkp-0000000B3II-3OsY; Mon, 24 Nov 2025 04:00:43 +0000 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1vNNkm-0000000B3HT-0Mcc for linux-nvme@lists.infradead.org; Mon, 24 Nov 2025 04:00:43 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1763956838; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=DdDKO8bUz7vs53nrnYdRyFnOzZ+W0EnIA6of8FyzT0A=; b=XAhAMA9GeUm6Ro30D7exmRuYYavWK0VxwlfdvL2GwKZ9mlRfAs143p0F0MCe1suMoTuNvi ThgMQD1SNhjSbkaX8KCysHgWlo0mehJoF1zUpVQrOpsJQjcc7Ab6o+0+xffJbaIRRulOGE mCBE031/YUBrAVkiEtzy+1xpALTxeLs= Received: from mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-44-SjJ7js_7NzGinyMRDNXk7w-1; Sun, 23 Nov 2025 23:00:32 -0500 X-MC-Unique: SjJ7js_7NzGinyMRDNXk7w-1 X-Mimecast-MFC-AGG-ID: SjJ7js_7NzGinyMRDNXk7w_1763956829 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 154B91800650; Mon, 24 Nov 2025 04:00:29 +0000 (UTC) Received: from fedora (unknown [10.72.116.227]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id CBC6319560B2; Mon, 24 Nov 2025 04:00:20 +0000 (UTC) Date: Mon, 24 Nov 2025 12:00:15 +0800 From: Ming Lei To: Mohamed Khalfella Cc: Jens Axboe , Keith Busch , Sagi Grimberg , Chaitanya Kulkarni , Casey Chen , Vikas Manocha , Yuanyuan Zhong , Hannes Reinecke , linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/1] nvme: Convert tag_list mutex to rwsemaphore to avoid deadlock Message-ID: References: <20251117202414.4071380-1-mkhalfella@purestorage.com> <20251117202414.4071380-2-mkhalfella@purestorage.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251117202414.4071380-2-mkhalfella@purestorage.com> X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251123_200040_222047_C0A26A4D X-CRM114-Status: GOOD ( 23.39 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On Mon, Nov 17, 2025 at 12:23:53PM -0800, Mohamed Khalfella wrote: > blk_mq_{add,del}_queue_tag_set() functions add and remove queues from > tagset, the functions make sure that tagset and queues are marked as > shared when two or more queues are attached to the same tagset. > Initially a tagset starts as unshared and when the number of added > queues reaches two, blk_mq_add_queue_tag_set() marks it as shared along > with all the queues attached to it. When the number of attached queues > drops to 1 blk_mq_del_queue_tag_set() need to mark both the tagset and > the remaining queues as unshared. > > Both functions need to freeze current queues in tagset before setting on > unsetting BLK_MQ_F_TAG_QUEUE_SHARED flag. While doing so, both functions > hold set->tag_list_lock mutex, which makes sense as we do not want > queues to be added or deleted in the process. This used to work fine > until commit 98d81f0df70c ("nvme: use blk_mq_[un]quiesce_tagset") > made the nvme driver quiesce tagset instead of quiscing individual > queues. blk_mq_quiesce_tagset() does the job and quiesce the queues in > set->tag_list while holding set->tag_list_lock also. > > This results in deadlock between two threads with these stacktraces: > > __schedule+0x48e/0xed0 > schedule+0x5a/0xc0 > schedule_preempt_disabled+0x11/0x20 > __mutex_lock.constprop.0+0x3cc/0x760 > blk_mq_quiesce_tagset+0x26/0xd0 > nvme_dev_disable_locked+0x77/0x280 [nvme] > nvme_timeout+0x268/0x320 [nvme] > blk_mq_handle_expired+0x5d/0x90 > bt_iter+0x7e/0x90 > blk_mq_queue_tag_busy_iter+0x2b2/0x590 > ? __blk_mq_complete_request_remote+0x10/0x10 > ? __blk_mq_complete_request_remote+0x10/0x10 > blk_mq_timeout_work+0x15b/0x1a0 > process_one_work+0x133/0x2f0 > ? mod_delayed_work_on+0x90/0x90 > worker_thread+0x2ec/0x400 > ? mod_delayed_work_on+0x90/0x90 > kthread+0xe2/0x110 > ? kthread_complete_and_exit+0x20/0x20 > ret_from_fork+0x2d/0x50 > ? kthread_complete_and_exit+0x20/0x20 > ret_from_fork_asm+0x11/0x20 > > __schedule+0x48e/0xed0 > schedule+0x5a/0xc0 > blk_mq_freeze_queue_wait+0x62/0x90 > ? destroy_sched_domains_rcu+0x30/0x30 > blk_mq_exit_queue+0x151/0x180 > disk_release+0xe3/0xf0 > device_release+0x31/0x90 > kobject_put+0x6d/0x180 > nvme_scan_ns+0x858/0xc90 [nvme_core] > ? nvme_scan_work+0x281/0x560 [nvme_core] > nvme_scan_work+0x281/0x560 [nvme_core] > process_one_work+0x133/0x2f0 > ? mod_delayed_work_on+0x90/0x90 > worker_thread+0x2ec/0x400 > ? mod_delayed_work_on+0x90/0x90 > kthread+0xe2/0x110 > ? kthread_complete_and_exit+0x20/0x20 > ret_from_fork+0x2d/0x50 > ? kthread_complete_and_exit+0x20/0x20 > ret_from_fork_asm+0x11/0x20 > > The top stacktrace is showing nvme_timeout() called to handle nvme > command timeout. timeout handler is trying to disable the controller and > as a first step, it needs to blk_mq_quiesce_tagset() to tell blk-mq not > to call queue callback handlers. The thread is stuck waiting for > set->tag_list_lock as it tires to walk the queues in set->tag_list. > > The lock is held by the second thread in the bottom stack which is > waiting for one of queues to be frozen. The queue usage counter will > drop to zero after nvme_timeout() finishes, and this will not happen > because the thread will wait for this mutex forever. > > Convert set->tag_list_lock mutex to set->tag_list_rwsem rwsemaphore to > avoid the deadlock. Update blk_mq_[un]quiesce_tagset() to take the > semaphore for read since this is enough to guarantee no queues will be > added or removed. Update blk_mq_{add,del}_queue_tag_set() to take the > semaphore for write while updating set->tag_list and downgrade it to > read while freezing the queues. It should be safe to update set->flags > and hctx->flags while holding the semaphore for read since the queues > are already frozen. > > Fixes: 98d81f0df70c ("nvme: use blk_mq_[un]quiesce_tagset") > Signed-off-by: Mohamed Khalfella Reviewed-by: Ming Lei Thanks, Ming