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Wed, 22 Apr 2020 02:06:41 +0000 (UTC) Received: from T590 (ovpn-8-28.pek2.redhat.com [10.72.8.28]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C797A58; Wed, 22 Apr 2020 02:06:31 +0000 (UTC) Date: Wed, 22 Apr 2020 10:06:25 +0800 From: Ming Lei To: Dexuan Cui Cc: "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 Subject: Re: [PATCH] scsi: storvsc: Fix a panic in the hibernation procedure Message-ID: <20200422020625.GD299948@T590> References: <1587514644-47058-1-git-send-email-decui@microsoft.com> <20200422012814.GB299948@T590> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Sender: linux-hyperv-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-hyperv@vger.kernel.org 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. Forget to mention, I guess that storvsc_suspend() may be called from runtime PM path, at that time, the whole system is running, and RCU can't be quick. Thanks, Ming