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Subject[PATCH v3] PCI: Lock the pci_cfg_wait queue for the consistency of data
Date
7ea7e98fd8d0 ("PCI: Block on access to temporarily unavailable pci
device") suggests that the "pci_lock" is sufficient, and all the
callers of pci_wait_cfg() are wrapped with the "pci_lock".

However, since the commit cdcb33f98244 ("PCI: Avoid possible deadlock on
pci_lock and p->pi_lock") merged, the accesses to the pci_cfg_wait queue
are not safe anymore. This would cause kernel panic in a very low chance
(See more detailed information from the below link). A "pci_lock" is
insufficient and we need to hold an additional queue lock while read/write
the wait queue.

So let's use the add_wait_queue()/remove_wait_queue() instead of
__add_wait_queue()/__remove_wait_queue(). Also move the wait queue
functionality around the "schedule()" function to avoid reintroducing
the deadlock addressed by "cdcb33f98244".

Signed-off-by: Xiang Zheng <zhengxiang9@huawei.com>
Cc: Heyi Guo <guoheyi@huawei.com>
Cc: Biaoxiang Ye <yebiaoxiang@huawei.com>
Link: https://lore.kernel.org/linux-pci/79827f2f-9b43-4411-1376-b9063b67aee3@huawei.com/
---

v3:
Improve the commit subject and message.

v2:
Move the wait queue functionality around the "schedule()".

---
drivers/pci/access.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/access.c b/drivers/pci/access.c
index 2fccb5762c76..09342a74e5ea 100644
--- a/drivers/pci/access.c
+++ b/drivers/pci/access.c
@@ -207,14 +207,14 @@ static noinline void pci_wait_cfg(struct pci_dev *dev)
{
DECLARE_WAITQUEUE(wait, current);

- __add_wait_queue(&pci_cfg_wait, &wait);
do {
set_current_state(TASK_UNINTERRUPTIBLE);
raw_spin_unlock_irq(&pci_lock);
+ add_wait_queue(&pci_cfg_wait, &wait);
schedule();
+ remove_wait_queue(&pci_cfg_wait, &wait);
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. */
--
2.19.1

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