From: Bjorn Helgaas bhelgaas@google.com
[ Upstream commit 2a7e32d0547f41c5ce244f84cf5d6ca7fccee7eb ]
The pci_cfg_wait queue is used to prevent user-space config accesses to devices while they are recovering from reset.
Previously we used these operations on pci_cfg_wait:
__add_wait_queue(&pci_cfg_wait, ...) __remove_wait_queue(&pci_cfg_wait, ...) wake_up_all(&pci_cfg_wait)
The wake_up acquires the wait queue lock, but the add and remove do not.
Originally these were all protected by the pci_lock, but cdcb33f98244 ("PCI: Avoid possible deadlock on pci_lock and p->pi_lock"), moved wake_up_all() outside pci_lock, so it could race with add/remove operations, which caused occasional kernel panics, e.g., during vfio-pci hotplug/unplug testing:
Unable to handle kernel read from unreadable memory at virtual address ffff802dac469000
Resolve this by using wait_event() instead of __add_wait_queue() and __remove_wait_queue(). The wait queue lock is held by both wait_event() and wake_up_all(), so it provides mutual exclusion.
Fixes: cdcb33f98244 ("PCI: Avoid possible deadlock on pci_lock and p->pi_lock") Link: https://lore.kernel.org/linux-pci/79827f2f-9b43-4411-1376-b9063b67aee3@huawe... Based-on: https://lore.kernel.org/linux-pci/20191210031527.40136-1-zhengxiang9@huawei.... Based-on-patch-by: Xiang Zheng zhengxiang9@huawei.com Signed-off-by: Bjorn Helgaas bhelgaas@google.com Tested-by: Xiang Zheng zhengxiang9@huawei.com Cc: Heyi Guo guoheyi@huawei.com Cc: Biaoxiang Ye yebiaoxiang@huawei.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/pci/access.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-)
diff --git a/drivers/pci/access.c b/drivers/pci/access.c index 7b5cf6d1181a9..6f2a07567532d 100644 --- a/drivers/pci/access.c +++ b/drivers/pci/access.c @@ -185,17 +185,13 @@ EXPORT_SYMBOL(pci_bus_set_ops); static DECLARE_WAIT_QUEUE_HEAD(pci_cfg_wait);
static noinline void pci_wait_cfg(struct pci_dev *dev) + __must_hold(&pci_lock) { - DECLARE_WAITQUEUE(wait, current); - - __add_wait_queue(&pci_cfg_wait, &wait); do { - set_current_state(TASK_UNINTERRUPTIBLE); raw_spin_unlock_irq(&pci_lock); - schedule(); + wait_event(pci_cfg_wait, !dev->block_cfg_access); raw_spin_lock_irq(&pci_lock); } while (dev->block_cfg_access); - __remove_wait_queue(&pci_cfg_wait, &wait); }
/* Returns 0 on success, negative values indicate error. */