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 X-Spam-Level: X-Spam-Status: No, score=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8D886C55181 for ; Wed, 22 Apr 2020 03:08:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6D39320722 for ; Wed, 22 Apr 2020 03:08:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1587524890; bh=00kZ49s3t3bAlBmeWs2Vc0CxVHkvA4fbM6GiSen4rQQ=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=XlC0/B6Wp9YxMipi8NgpTl+sJuR6rU9+dT5C9sIg+OLR4uhmTgyiseee1c/e4l5W2 gs4zcK607bAO9hRDLf0+coa+PdCEhK1MxBLZFiBX3u9pKR42bUcKgoAWZH2EGdl02y aAgGPH963QLJ3l2+ea+brAEEkB7cODAtRwHM62aE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726396AbgDVDIJ (ORCPT ); Tue, 21 Apr 2020 23:08:09 -0400 Received: from mail.kernel.org ([198.145.29.99]:40768 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726228AbgDVDIJ (ORCPT ); Tue, 21 Apr 2020 23:08:09 -0400 Received: from paulmck-ThinkPad-P72.home (50-39-105-78.bvtn.or.frontiernet.net [50.39.105.78]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 1D89E2070B; Wed, 22 Apr 2020 03:08:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1587524888; bh=00kZ49s3t3bAlBmeWs2Vc0CxVHkvA4fbM6GiSen4rQQ=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=wfdApLvE/3xwrwCtPcMQr1rL34+cx7YSXiAQccBXOmD97IxVPg3SHSlvcCwDOWfZk ZTrE+akF4LIqOg7mcI7UOXl/+wNfTSzxk0aqcnnRvo677IluDAh759XEb3Baz0um7u fOmSCBtBUImQw/YC+HStUtsAapP4pnoE5LDuh45o= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id F3BCE35226E4; Tue, 21 Apr 2020 20:08:07 -0700 (PDT) Date: Tue, 21 Apr 2020 20:08:07 -0700 From: "Paul E. McKenney" To: Ming Lei Cc: Dexuan Cui , Josh Triplett , "Rafael J. Wysocki" , "jejb@linux.ibm.com" , "martin.petersen@oracle.com" , "linux-scsi@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "hch@lst.de" , "bvanassche@acm.org" , "hare@suse.de" , Michael Kelley , Long Li , "linux-hyperv@vger.kernel.org" , "wei.liu@kernel.org" , Stephen Hemminger , Haiyang Zhang , KY Srinivasan , linux-pm@vger.kernel.org Subject: Re: [PATCH] scsi: storvsc: Fix a panic in the hibernation procedure Message-ID: <20200422030807.GK17661@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <1587514644-47058-1-git-send-email-decui@microsoft.com> <20200422012814.GB299948@T590> <20200422020134.GC299948@T590> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200422020134.GC299948@T590> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 22, 2020 at 10:01:34AM +0800, Ming Lei wrote: > On Wed, Apr 22, 2020 at 01:48:25AM +0000, Dexuan Cui wrote: > > > From: Ming Lei > > > Sent: Tuesday, April 21, 2020 6:28 PM > > > To: Dexuan Cui > > > > > > On Tue, Apr 21, 2020 at 05:17:24PM -0700, Dexuan Cui wrote: > > > > During hibernation, the sdevs are suspended automatically in > > > > drivers/scsi/scsi_pm.c before storvsc_suspend(), so after > > > > storvsc_suspend(), there is no disk I/O from the file systems, but there > > > > can still be disk I/O from the kernel space, e.g. disk_check_events() -> > > > > sr_block_check_events() -> cdrom_check_events() can still submit I/O > > > > to the storvsc driver, which causes a paic of NULL pointer dereference, > > > > since storvsc has closed the vmbus channel in storvsc_suspend(): refer > > > > to the below links for more info: > > > > > > > > Fix the panic by blocking/unblocking all the I/O queues properly. > > > > > > > > Note: this patch depends on another patch "scsi: core: Allow the state > > > > change from SDEV_QUIESCE to SDEV_BLOCK" (refer to the second link > > > above). > > > > > > > > Fixes: 56fb10585934 ("scsi: storvsc: Add the support of hibernation") > > > > Signed-off-by: Dexuan Cui > > > > --- > > > > drivers/scsi/storvsc_drv.c | 10 ++++++++++ > > > > 1 file changed, 10 insertions(+) > > > > > > > > diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c > > > > index fb41636519ee..fd51d2f03778 100644 > > > > --- a/drivers/scsi/storvsc_drv.c > > > > +++ b/drivers/scsi/storvsc_drv.c > > > > @@ -1948,6 +1948,11 @@ static int storvsc_suspend(struct hv_device > > > *hv_dev) > > > > struct storvsc_device *stor_device = hv_get_drvdata(hv_dev); > > > > struct Scsi_Host *host = stor_device->host; > > > > struct hv_host_device *host_dev = shost_priv(host); > > > > + int ret; > > > > + > > > > + ret = scsi_host_block(host); > > > > + if (ret) > > > > + return ret; > > > > > > > > storvsc_wait_to_drain(stor_device); > > > > > > > > @@ -1968,10 +1973,15 @@ static int storvsc_suspend(struct hv_device > > > *hv_dev) > > > > > > > > static int storvsc_resume(struct hv_device *hv_dev) > > > > { > > > > + struct storvsc_device *stor_device = hv_get_drvdata(hv_dev); > > > > + struct Scsi_Host *host = stor_device->host; > > > > int ret; > > > > > > > > ret = storvsc_connect_to_vsp(hv_dev, storvsc_ringbuffer_size, > > > > hv_dev_is_fc(hv_dev)); > > > > + if (!ret) > > > > + ret = scsi_host_unblock(host, SDEV_RUNNING); > > > > + > > > > return ret; > > > > } > > > > > > scsi_host_block() is actually too heavy for just avoiding > > > scsi internal command, which can be done simply by one atomic > > > variable. > > > > > > Not mention scsi_host_block() is implemented too clumsy because > > > nr_luns * synchronize_rcu() are required in scsi_host_block(), > > > which should have been optimized to just one. > > > > > > Also scsi_device_quiesce() is heavy too, still takes 2 > > > synchronize_rcu() for one LUN. > > > > > > That is said SCSI suspend may take (3 * nr_luns) sysnchronize_rcu() in > > > case that the HBA's suspend handler needs scsi_host_block(). > > > > > > Thanks, > > > Ming > > > > When we're in storvsc_suspend(), all the userspace processes have been > > frozen and all the file systems have been flushed, and there should not > > be too much I/O from the kernel space, so IMO scsi_host_block() should be > > pretty fast here. > > I guess it depends on RCU's implementation, so CC RCU guys. > > Hello Paul & Josh, > > Could you clarify that if sysnchronize_rcu becomes quickly during > system suspend? Once you have all but one CPU offlined, it becomes extremely fast, as in roughly a no-op (which is an idea of Josh's from back in the day). But if there is more than one CPU online, then synchronize_rcu() still takes on the order of several to several tens of jiffies. So, yes, in some portions of system suspend, synchronize_rcu() becomes very fast indeed. Thanx, Paul