[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v4 2/5] xen/pciback: Don't deadlock when unbinding.
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 <konrad.wilk@xxxxxxxxxx> 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 <konrad.wilk@xxxxxxxxxx> --- [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 <boris.ostrovsky@xxxxxxxxxx>(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 _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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