From e8801a7418dda995a70f30874aef77e6d064828e Mon Sep 17 00:00:00 2001 From: Konrad Rzeszutek Wilk Date: Wed, 3 Dec 2014 16:40:26 -0500 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. Reviewed-by: Boris Ostrovsky Signed-off-by: Konrad Rzeszutek Wilk Signed-off-by: David Vrabel --- drivers/xen/xen-pciback/passthrough.c | 14 +++++++++++--- drivers/xen/xen-pciback/pci_stub.c | 12 ++++++------ drivers/xen/xen-pciback/pciback.h | 7 ++++--- drivers/xen/xen-pciback/vpci.c | 14 +++++++++++--- drivers/xen/xen-pciback/xenbus.c | 2 +- 5 files changed, 33 insertions(+), 16 deletions(-) diff --git a/drivers/xen/xen-pciback/passthrough.c b/drivers/xen/xen-pciback/passthrough.c index 828dddc360df..f16a30e2a110 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) @@ -156,8 +161,11 @@ static void __xen_pcibk_release_devices(struct xen_pcibk_device *pdev) struct pci_dev_entry *dev_entry, *t; list_for_each_entry_safe(dev_entry, t, &dev_data->dev_list, list) { + struct pci_dev *dev = dev_entry->dev; list_del(&dev_entry->list); - pcistub_put_pci_dev(dev_entry->dev); + device_lock(&dev->dev); + pcistub_put_pci_dev(dev); + device_unlock(&dev->dev); kfree(dev_entry); } diff --git a/drivers/xen/xen-pciback/pci_stub.c b/drivers/xen/xen-pciback/pci_stub.c index 017069a455d4..9cbe1a31c1e5 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 f72af87640e0..58e38d586f52 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 51afff96c515..c99f8bb1c56c 100644 --- a/drivers/xen/xen-pciback/vpci.c +++ b/drivers/xen/xen-pciback/vpci.c @@ -145,7 +145,7 @@ 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) { 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) @@ -208,8 +213,11 @@ static void __xen_pcibk_release_devices(struct xen_pcibk_device *pdev) struct pci_dev_entry *e, *tmp; list_for_each_entry_safe(e, tmp, &vpci_dev->dev_list[slot], list) { + struct pci_dev *dev = e->dev; list_del(&e->list); - pcistub_put_pci_dev(e->dev); + device_lock(&dev->dev); + pcistub_put_pci_dev(dev); + device_unlock(&dev->dev); kfree(e); } } diff --git a/drivers/xen/xen-pciback/xenbus.c b/drivers/xen/xen-pciback/xenbus.c index ad8d30c088fe..eeee499d4b3c 100644 --- a/drivers/xen/xen-pciback/xenbus.c +++ b/drivers/xen/xen-pciback/xenbus.c @@ -291,7 +291,7 @@ 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;