PCI: Fix pci_cfg_wait queue locking problem

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/[email protected]/T/#u
Based-on: https://lore.kernel.org/linux-pci/[email protected]/
Based-on-patch-by: Xiang Zheng <[email protected]>
Signed-off-by: Bjorn Helgaas <[email protected]>
Tested-by: Xiang Zheng <[email protected]>
Cc: Heyi Guo <[email protected]>
Cc: Biaoxiang Ye <[email protected]>

0 files changed, 0 insertions, 0 deletions