From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752103AbaHDSm6 (ORCPT ); Mon, 4 Aug 2014 14:42:58 -0400 Received: from aserp1040.oracle.com ([141.146.126.69]:31727 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751163AbaHDSm4 (ORCPT ); Mon, 4 Aug 2014 14:42:56 -0400 Date: Mon, 4 Aug 2014 14:42:47 -0400 From: Konrad Rzeszutek Wilk To: David Vrabel Cc: gregkh@linuxfoundation.org, xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org, boris.ostrovsky@oracle.com, stable@vger.kernel.org Subject: Re: [PATCH v5 2/6] xen/pciback: Don't deadlock when unbinding. Message-ID: <20140804184247.GA9009@laptop.dumpdata.com> References: <1405354736-7358-1-git-send-email-konrad.wilk@oracle.com> <1405354736-7358-3-git-send-email-konrad.wilk@oracle.com> <53D64AF3.4080202@citrix.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <53D64AF3.4080202@citrix.com> User-Agent: Mutt/1.5.23 (2014-03-12) X-Source-IP: acsinet21.oracle.com [141.146.126.237] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 28, 2014 at 02:06:59PM +0100, David Vrabel wrote: > On 14/07/14 17:18, Konrad Rzeszutek Wilk wrote: > > As commit 0a9fd0152929db372ff61b0d6c280fdd34ae8bdb > > 'xen/pciback: Document the entry points for 'pcistub_put_pci_dev'' > > explained there are four entry points in this function. > > Two of them are when the user fiddles in the SysFS to > > unbind a device which might be in use by a guest or not. > > > > Both 'unbind' states will cause a deadlock as the the PCI lock has > > already been taken, which then pci_device_reset tries to take. > > > > We can simplify this by requiring that all callers of > > pcistub_put_pci_dev MUST hold the device lock. And then > > we can just call the lockless version of pci_device_reset. > > > > To make it even simpler we will modify xen_pcibk_release_pci_dev > > to quality whether it should take a lock or not - as it ends > > up calling xen_pcibk_release_pci_dev and needs to hold the lock. > > > > CC: stable@vger.kernel.org > > This deadlock is for a rather specific and uncommon use case (manually > unbinding a PCI while it is passed-through). Is this critical enough to > warrant a stable backport? We seem to trip over it frequently when rebooting a server. That is the VF's end up being unbinded while the guests are being shutdown. And depending on the timing we end up in a deadlock. > > > Reviewed-by: Boris Ostrovsky > > Signed-off-by: Konrad Rzeszutek Wilk > > Reviewed-by: David Vrabel > > David