[PATCH 4.9 033/167] PCI: Avoid pci_dev_lock() AB/BA deadlock with sriov_numvfs_store()

Greg Kroah-Hartman
2022-06-13T10:16:28Z

From: Yicong Yang <yangyicong@hisilicon.com>

[ Upstream commit a91ee0e9fca9d7501286cfbced9b30a33e52740a ]

The sysfs sriov_numvfs_store() path acquires the device lock before the
config space access lock:

sriov_numvfs_store
device_lock # A (1) acquire device lock
sriov_configure
vfio_pci_sriov_configure # (for example)
vfio_pci_core_sriov_configure
pci_disable_sriov
sriov_disable
pci_cfg_access_lock
pci_wait_cfg # B (4) wait for dev->block_cfg_access == 0

Previously, pci_dev_lock() acquired the config space access lock before the
device lock:

pci_dev_lock
pci_cfg_access_lock
dev->block_cfg_access = 1 # B (2) set dev->block_cfg_access = 1
device_lock # A (3) wait for device lock

Any path that uses pci_dev_lock(), e.g., pci_reset_function(), may
deadlock with sriov_numvfs_store() if the operations occur in the sequence
(1) (2) (3) (4).

Avoid the deadlock by reversing the order in pci_dev_lock() so it acquires
the device lock before the config space access lock, the same as the
sriov_numvfs_store() path.

[bhelgaas: combined and adapted commit log from Jay Zhou's independent
subsequent posting:
https://lore.kernel.org/r/20220404062539.1710-1-jianjay.zhou@huawei.com]
Link: https://lore.kernel.org/linux-pci/1583489997-17156-1-git-send-email-yangyicong@hisilicon.com/
Also-posted-by: Jay Zhou <jianjay.zhou@huawei.com>
Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/pci/pci.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 2cf13578fe75..e6e0012269cd 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -4079,18 +4079,18 @@ static int __pci_dev_reset(struct pci_dev *dev, int probe)

static void pci_dev_lock(struct pci_dev *dev)
{
- pci_cfg_access_lock(dev);
/* block PM suspend, driver probe, etc. */
device_lock(&dev->dev);
+ pci_cfg_access_lock(dev);
}

/* Return 1 on successful lock, 0 on contention */
static int pci_dev_trylock(struct pci_dev *dev)
{
- if (pci_cfg_access_trylock(dev)) {
- if (device_trylock(&dev->dev))
+ if (device_trylock(&dev->dev)) {
+ if (pci_cfg_access_trylock(dev))
return 1;
- pci_cfg_access_unlock(dev);
+ device_unlock(&dev->dev);
}

return 0;
@@ -4098,8 +4098,8 @@ static int pci_dev_trylock(struct pci_dev *dev)

static void pci_dev_unlock(struct pci_dev *dev)
{
- device_unlock(&dev->dev);
pci_cfg_access_unlock(dev);
+ device_unlock(&dev->dev);
}

/**
--
2.35.1