[PATCH] xen/pciback: Don't deadlock when unbinding.
From: Konrad Rzeszutek Wilk
Date: Tue Jul 08 2014 - 11:12:02 EST
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);
/* 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
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