Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755873AbaGNO2N (ORCPT ); Mon, 14 Jul 2014 10:28:13 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:32776 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755836AbaGNO2B (ORCPT ); Mon, 14 Jul 2014 10:28:01 -0400 Message-ID: <53C3E975.60900@oracle.com> Date: Mon, 14 Jul 2014 10:30:13 -0400 From: Boris Ostrovsky User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: Konrad Rzeszutek Wilk CC: konrad@kernel.org, xen-devel@lists.xenproject.org, david.vrabel@citrix.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 2/5] xen/pciback: Don't deadlock when unbinding. References: <1405109332-31659-1-git-send-email-konrad@kernel.org> <1405109332-31659-3-git-send-email-konrad@kernel.org> <53C04D81.3010002@oracle.com> <20140711210201.GC25233@laptop.dumpdata.com> <20140714141328.GA5112@laptop.dumpdata.com> In-Reply-To: <20140714141328.GA5112@laptop.dumpdata.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit 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 07/14/2014 10:13 AM, Konrad Rzeszutek Wilk wrote: > On Fri, Jul 11, 2014 at 05:02:01PM -0400, Konrad Rzeszutek Wilk wrote: >>>> --- a/drivers/xen/xen-pciback/pci_stub.c >>>> +++ b/drivers/xen/xen-pciback/pci_stub.c >>>> @@ -250,6 +250,8 @@ struct pci_dev *pcistub_get_pci_dev(struct xen_pcibk_device *pdev, >>>> * - 'echo BDF > unbind' with a guest still using it. See pcistub_remove >>>> * >>>> * As such we have to be careful. >>>> + * >>>> + * To make this easier, the caller has to hold the device lock. >>> Should we assert that the lock is being held? >> Yes of course we should. Thank you! > How about this: > > From 388a03c598218dac8bfeb6c5bf3992e0d1e37d1e Mon Sep 17 00:00:00 2001 > From: Konrad Rzeszutek Wilk > Date: Tue, 8 Jul 2014 11:12:02 -0400 > Subject: [PATCH] xen/pciback: Don't deadlock when unbinding. > > 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. > > Signed-off-by: Konrad Rzeszutek Wilk > --- > [v2: Per David Vrabel's suggestion - use lockless version of reset] > [v3: Per Boris suggestion add assertion mechanism] > --- > drivers/xen/xen-pciback/passthrough.c | 9 +++++++-- > drivers/xen/xen-pciback/pci_stub.c | 12 ++++++------ > drivers/xen/xen-pciback/pciback.h | 7 ++++--- > drivers/xen/xen-pciback/vpci.c | 9 +++++++-- > drivers/xen/xen-pciback/xenbus.c | 2 +- > 5 files changed, 25 insertions(+), 14 deletions(-) > > diff --git a/drivers/xen/xen-pciback/passthrough.c b/drivers/xen/xen-pciback/passthrough.c > index 828dddc..d0c3fb4 100644 > --- a/drivers/xen/xen-pciback/passthrough.c > +++ b/drivers/xen/xen-pciback/passthrough.c > @@ -69,7 +69,7 @@ static int __xen_pcibk_add_pci_dev(struct xen_pcibk_device *pdev, > } > > static void __xen_pcibk_release_pci_dev(struct xen_pcibk_device *pdev, > - struct pci_dev *dev) > + struct pci_dev *dev, bool lock) > { > struct passthrough_dev_data *dev_data = pdev->pci_dev_data; > struct pci_dev_entry *dev_entry, *t; > @@ -87,8 +87,13 @@ static void __xen_pcibk_release_pci_dev(struct xen_pcibk_device *pdev, > > mutex_unlock(&dev_data->lock); > > - if (found_dev) > + if (found_dev) { > + if (lock) > + device_lock(&found_dev->dev); > pcistub_put_pci_dev(found_dev); > + if (lock) > + device_unlock(&found_dev->dev); > + } > } > > static int __xen_pcibk_init_devices(struct xen_pcibk_device *pdev) > diff --git a/drivers/xen/xen-pciback/pci_stub.c b/drivers/xen/xen-pciback/pci_stub.c > index d57a173..8293fbb 100644 > --- a/drivers/xen/xen-pciback/pci_stub.c > +++ b/drivers/xen/xen-pciback/pci_stub.c > @@ -250,6 +250,8 @@ struct pci_dev *pcistub_get_pci_dev(struct xen_pcibk_device *pdev, > * - 'echo BDF > unbind' with a guest still using it. See pcistub_remove > * > * As such we have to be careful. > + * > + * To make this easier, the caller has to hold the device lock. > */ > void pcistub_put_pci_dev(struct pci_dev *dev) > { > @@ -276,11 +278,8 @@ void pcistub_put_pci_dev(struct pci_dev *dev) > /* Cleanup our device > * (so it's ready for the next domain) > */ > - > - /* This is OK - we are running from workqueue context > - * and want to inhibit the user from fiddling with 'reset' > - */ > - pci_reset_function(dev); > + lockdep_assert_held(&dev->dev.mutex); > + __pci_reset_function_locked(dev); > pci_restore_state(dev); Reviewed-by: Boris Ostrovsky (Although I wonder about the fact that we are exposing the mutex which is typically hidden by device_lock()/unlock() inlines. Have you considered adding something like is_device_locked() to device.h?) -boris -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/