Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753545AbaGKUpv (ORCPT ); Fri, 11 Jul 2014 16:45:51 -0400 Received: from aserp1040.oracle.com ([141.146.126.69]:47857 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751507AbaGKUpu (ORCPT ); Fri, 11 Jul 2014 16:45:50 -0400 Message-ID: <53C04D81.3010002@oracle.com> Date: Fri, 11 Jul 2014 16:48:01 -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@kernel.org, xen-devel@lists.xenproject.org, david.vrabel@citrix.com, linux-kernel@vger.kernel.org CC: Konrad Rzeszutek Wilk 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> In-Reply-To: <1405109332-31659-3-git-send-email-konrad@kernel.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit 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 07/11/2014 04:08 PM, konrad@kernel.org wrote: > From: Konrad Rzeszutek Wilk > > 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] > --- > drivers/xen/xen-pciback/passthrough.c | 9 +++++++-- > drivers/xen/xen-pciback/pci_stub.c | 11 +++++------ > drivers/xen/xen-pciback/pciback.h | 7 ++++--- > drivers/xen/xen-pciback/vpci.c | 9 +++++++-- > drivers/xen/xen-pciback/xenbus.c | 2 +- > 5 files changed, 24 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..eebbb41 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. Should we assert that the lock is being held? -boris > */ > void pcistub_put_pci_dev(struct pci_dev *dev) > { > @@ -276,11 +278,7 @@ 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); > + __pci_reset_function_locked(dev); > pci_restore_state(dev); > > /* This disables the device. */ > @@ -567,7 +565,8 @@ 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..065aae8 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; -- 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/