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 14913D74956 for ; Wed, 30 Oct 2024 02:20:57 +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:Content-Type:In-Reply-To: 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=kr+RlyJzlDlKj1PHdM+HAqRlXCduR8MkPt7tryONwYg=; b=ZTI9UD9UCutRo48t9017RLdnGZ BIk9UZ7yjjminVJjdPMMxtM+ciVOm2dpxYQG1zbRbfoFMeOKc/u8ouO7vRzr49ehDlUAfLQJ0e3RV kJLgL+pCHPpZn8Dm6vveJHdL02JhIHMsVnelc0CpMVnyxyGznIxkkB2k1J6mX9DyrM0WtiokRK8H9 nslMvSdVBSXf0+3Kuq4kQR7Bv022Bby4/BYikHbWyJS0xq4HLBu+79eiHU/hS0YD+syTndm5mV16z uNFTT4vCZasYsrac3W4vFK3sriXzXVjBTCwcRxcmahIRkb+m+KZyc+A3n5Rg/wV+AG9RF3vSgdrcX GHMsi88w==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1t5yKL-0000000GVX8-3FjR; Wed, 30 Oct 2024 02:20:53 +0000 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by bombadil.infradead.org with esmtps (Exim 4.98 #2 (Red Hat Linux)) id 1t5yKI-0000000GVWj-1PIe for linux-nvme@lists.infradead.org; Wed, 30 Oct 2024 02:20:52 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1730254848; 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=kr+RlyJzlDlKj1PHdM+HAqRlXCduR8MkPt7tryONwYg=; b=WH5+xHlhotCL3MhsK74bPIFAaSWY87D54rzhmqQheLGP68emULgdU6hGE08HoG790PGB2H yy80+YN9/tBWZvnHfDxxd+opWD9aDa/k+d3d/4EC+RSetspT+IM+bchOl845FSI2lVf3Uj UvYfqaW2kXlJgJTAypN4ubpj5q/Zt5E= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-34-HC08kHqZPBOSfJ1wOyMjdQ-1; Tue, 29 Oct 2024 22:20:47 -0400 X-MC-Unique: HC08kHqZPBOSfJ1wOyMjdQ-1 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-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id D3C7319560BE; Wed, 30 Oct 2024 02:20:45 +0000 (UTC) Received: from fedora (unknown [10.72.116.45]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id A94FE19560A2; Wed, 30 Oct 2024 02:20:39 +0000 (UTC) Date: Wed, 30 Oct 2024 10:20:34 +0800 From: Ming Lei To: Nilay Shroff Cc: linux-nvme@lists.infradead.org, kbusch@kernel.org, hch@lst.de, sagi@grimberg.me, axboe@fb.com, chaitanyak@nvidia.com, dlemoal@kernel.org, gjoyce@linux.ibm.com Subject: Re: [PATCH 2/3] nvme-fabrics: fix kernel crash while shutting down controller Message-ID: References: <20241027170209.440776-1-nilay@linux.ibm.com> <20241027170209.440776-3-nilay@linux.ibm.com> MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20241029_192050_473513_66FD1DA0 X-CRM114-Status: GOOD ( 40.73 ) 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 Tue, Oct 29, 2024 at 06:10:00PM +0530, Nilay Shroff wrote: > > > On 10/29/24 12:53, Ming Lei wrote: > > On Sun, Oct 27, 2024 at 10:32:05PM +0530, Nilay Shroff wrote: > >> The nvme keep-alive operation, which executes at a periodic interval, > >> could potentially sneak in while shutting down a fabric controller. > >> This may lead to a race between the fabric controller admin queue > >> destroy code path (invoked while shutting down controller) and hw/hctx > >> queue dispatcher called from the nvme keep-alive async request queuing > >> operation. This race could lead to the kernel crash shown below: > >> > >> Call Trace: > >> autoremove_wake_function+0x0/0xbc (unreliable) > >> __blk_mq_sched_dispatch_requests+0x114/0x24c > >> blk_mq_sched_dispatch_requests+0x44/0x84 > >> blk_mq_run_hw_queue+0x140/0x220 > >> nvme_keep_alive_work+0xc8/0x19c [nvme_core] > >> process_one_work+0x200/0x4e0 > >> worker_thread+0x340/0x504 > >> kthread+0x138/0x140 > >> start_kernel_thread+0x14/0x18 > >> > >> While shutting down fabric controller, if nvme keep-alive request sneaks > >> in then it would be flushed off. The nvme_keep_alive_end_io function is > >> then invoked to handle the end of the keep-alive operation which > >> decrements the admin->q_usage_counter and assuming this is the last/only > >> request in the admin queue then the admin->q_usage_counter becomes zero. > >> If that happens then blk-mq destroy queue operation (blk_mq_destroy_ > >> queue()) which could be potentially running simultaneously on another > >> cpu (as this is the controller shutdown code path) would forward > >> progress and deletes the admin queue. So, now from this point onward > >> we are not supposed to access the admin queue resources. However the > >> issue here's that the nvme keep-alive thread running hw/hctx queue > >> dispatch operation hasn't yet finished its work and so it could still > >> potentially access the admin queue resource while the admin queue had > >> been already deleted and that causes the above crash. > >> > >> The above kernel crash is regression caused due to changes implemented > >> in commit a54a93d0e359 ("nvme: move stopping keep-alive into > >> nvme_uninit_ctrl()"). Ideally we should stop keep-alive at the very > >> beggining of the controller shutdown code path so that it wouldn't > >> sneak in during the shutdown operation. However we removed the keep > >> alive stop operation from the beginning of the controller shutdown > >> code path in commit a54a93d0e359 ("nvme: move stopping keep-alive into > >> nvme_uninit_ctrl()") and that now created the possibility of keep-alive > >> sneaking in and interfering with the shutdown operation and causing > >> observed kernel crash. So to fix this crash, now we're adding back the > >> keep-alive stop operation at very beginning of the fabric controller > >> shutdown code path so that the actual controller shutdown opeation only > >> begins after it's ensured that keep-alive operation is not in-flight and > >> also it can't be scheduled in future. > >> > >> Fixes: a54a93d0e359 ("nvme: move stopping keep-alive into nvme_uninit_ctrl()") > >> Link: https://lore.kernel.org/all/196f4013-3bbf-43ff-98b4-9cb2a96c20c2@grimberg.me/#t > >> Signed-off-by: Nilay Shroff > >> --- > >> drivers/nvme/host/core.c | 5 +++++ > >> 1 file changed, 5 insertions(+) > >> > >> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c > >> index 5016f69e9a15..865c00ea19e3 100644 > >> --- a/drivers/nvme/host/core.c > >> +++ b/drivers/nvme/host/core.c > >> @@ -4648,6 +4648,11 @@ void nvme_stop_ctrl(struct nvme_ctrl *ctrl) > >> { > >> nvme_mpath_stop(ctrl); > >> nvme_auth_stop(ctrl); > >> + /* > >> + * the transport driver may be terminating the admin tagset a little > >> + * later on, so we cannot have the keep-alive work running > >> + */ > >> + nvme_stop_keep_alive(ctrl); > >> nvme_stop_failfast_work(ctrl); > >> flush_work(&ctrl->async_event_work); > >> cancel_work_sync(&ctrl->fw_act_work); > > > > The change looks fine. > > > > IMO the `nvme_stop_keep_alive` in nvme_uninit_ctrl() may be moved to > > entry of nvme_remove_admin_tag_set(), then this one in nvme_stop_ctrl() > > can be saved? > > > Yes that should work however IMO, stopping keep-alive at very beginning of > shutdown operation would make sense because delaying the stopping of keep-alive > would not be useful anyways once we start the controller shutdown. It may > sneak in unnecessarily while we shutdown controller and later we will have to > flush it off. > > And yes, as you mentioned, in this case we would save one call site but > looking at the code we have few other call sites already present where we > call nvme_stop_keep_alive(). If it works, I'd suggest to move nvme_stop_keep_alive() from nvme_uninit_ctrl() into nvme_remove_admin_tag_set() because: 1) it isn't correct to do it in nvme_uninit_ctrl() 2) stop keep alive in nvme_remove_admin_tag_set() covers everything 3) most of nvme_stop_keep_alive() can be removed in failure path Thanks, Ming