On Tue, Nov 19, 2019 at 09:15:45AM +0800, Xiang Zheng wrote:
> Commit "7ea7e98fd8d0" 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" merged, the accesses to
> the pci_cfg_wait queue are not safe anymore. 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".
Procedural nits:
- Run "git log --oneline drivers/pci/access.c" and follow the
convention, e.g., starts with "PCI: " and first subsequent word is
capitalized.
- Use conventional commit references, e.g., 7ea7e98fd8d0 ("PCI:
Block on access to temporarily unavailable pci device") and
cdcb33f98244 ("PCI: Avoid possible deadlock on pci_lock and
p->pi_lock")
- IIRC you found that this actually caused a panic; please include
the lore.kernel.org URL to that report.
You can wait for a while to see if there are more substantive comments
to address before posting a v3.
> Signed-off-by: Xiang Zheng <zhengxiang9@xxxxxxxxxx>
> Cc: Heyi Guo <guoheyi@xxxxxxxxxx>
> Cc: Biaoxiang Ye <yebiaoxiang@xxxxxxxxxx>
> ---
>
> v2:
> - Move the wait queue functionality around the "schedule()" function to
> avoid reintroducing the deadlock addressed by "cdcb33f98244"
>
> ---
>
> 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
>
>
