Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755716AbaGNONs (ORCPT ); Mon, 14 Jul 2014 10:13:48 -0400 Received: from aserp1040.oracle.com ([141.146.126.69]:31411 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755694AbaGNONj (ORCPT ); Mon, 14 Jul 2014 10:13:39 -0400 Date: Mon, 14 Jul 2014 10:13:28 -0400 From: Konrad Rzeszutek Wilk To: Boris Ostrovsky 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. Message-ID: <20140714141328.GA5112@laptop.dumpdata.com> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140711210201.GC25233@laptop.dumpdata.com> User-Agent: Mutt/1.5.23 (2014-03-12) X-Source-IP: ucsinet21.oracle.com [156.151.31.93] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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); /* This disables the device. */ @@ -567,7 +566,8 @@ static void pcistub_remove(struct pci_dev *dev) /* N.B. This ends up calling pcistub_put_pci_dev which ends up * doing the FLR. */ xen_pcibk_release_pci_dev(found_psdev->pdev, - found_psdev->dev); + found_psdev->dev, + false /* caller holds the lock. */); } spin_lock_irqsave(&pcistub_devices_lock, flags); diff --git a/drivers/xen/xen-pciback/pciback.h b/drivers/xen/xen-pciback/pciback.h index f72af87..58e38d5 100644 --- a/drivers/xen/xen-pciback/pciback.h +++ b/drivers/xen/xen-pciback/pciback.h @@ -99,7 +99,8 @@ struct xen_pcibk_backend { unsigned int *domain, unsigned int *bus, unsigned int *devfn); int (*publish)(struct xen_pcibk_device *pdev, publish_pci_root_cb cb); - void (*release)(struct xen_pcibk_device *pdev, struct pci_dev *dev); + void (*release)(struct xen_pcibk_device *pdev, struct pci_dev *dev, + bool lock); int (*add)(struct xen_pcibk_device *pdev, struct pci_dev *dev, int devid, publish_pci_dev_cb publish_cb); struct pci_dev *(*get)(struct xen_pcibk_device *pdev, @@ -122,10 +123,10 @@ static inline int xen_pcibk_add_pci_dev(struct xen_pcibk_device *pdev, } static inline void xen_pcibk_release_pci_dev(struct xen_pcibk_device *pdev, - struct pci_dev *dev) + struct pci_dev *dev, bool lock) { if (xen_pcibk_backend && xen_pcibk_backend->release) - return xen_pcibk_backend->release(pdev, dev); + return xen_pcibk_backend->release(pdev, dev, lock); } static inline struct pci_dev * diff --git a/drivers/xen/xen-pciback/vpci.c b/drivers/xen/xen-pciback/vpci.c index 51afff9..2fdfcb9 100644 --- a/drivers/xen/xen-pciback/vpci.c +++ b/drivers/xen/xen-pciback/vpci.c @@ -145,7 +145,7 @@ out: } static void __xen_pcibk_release_pci_dev(struct xen_pcibk_device *pdev, - struct pci_dev *dev) + struct pci_dev *dev, bool lock) { int slot; struct vpci_dev_data *vpci_dev = pdev->pci_dev_data; @@ -169,8 +169,13 @@ static void __xen_pcibk_release_pci_dev(struct xen_pcibk_device *pdev, out: mutex_unlock(&vpci_dev->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/xenbus.c b/drivers/xen/xen-pciback/xenbus.c index 4a7e6e0..b3318fd 100644 --- a/drivers/xen/xen-pciback/xenbus.c +++ b/drivers/xen/xen-pciback/xenbus.c @@ -290,7 +290,7 @@ static int xen_pcibk_remove_device(struct xen_pcibk_device *pdev, /* N.B. This ends up calling pcistub_put_pci_dev which ends up * doing the FLR. */ - xen_pcibk_release_pci_dev(pdev, dev); + xen_pcibk_release_pci_dev(pdev, dev, true /* use the lock. */); out: return err; -- 1.9.3 -- 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/