Re: [PATCH RESEND] nvme-pci: Fix EEH failure on ppc after subsystem reset

Keith Busch
2024-03-09T15:44:56Z

On Sat, Mar 09, 2024 at 07:59:11PM +0530, Nilay Shroff wrote:
> On 3/8/24 21:11, Keith Busch wrote:
> > On Fri, Feb 09, 2024 at 10:32:16AM +0530, Nilay Shroff wrote:
> >> @@ -2776,6 +2776,14 @@ static void nvme_reset_work(struct work_struct *work)
> >> out_unlock:
> >> mutex_unlock(&dev->shutdown_lock);
> >> out:
> >> + /*
> >> + * If PCI recovery is ongoing then let it finish first
> >> + */
> >> + if (pci_channel_offline(to_pci_dev(dev->dev))) {
> >> + dev_warn(dev->ctrl.device, "PCI recovery is ongoing so let it finish\n");
> >> + return;
> >> + }
> >> +
> >> /*
> >> * Set state to deleting now to avoid blocking nvme_wait_reset(), which
> >> * may be holding this pci_dev's device lock.
> >> @@ -3295,9 +3303,11 @@ static pci_ers_result_t nvme_error_detected(struct pci_dev *pdev,
> >> case pci_channel_io_frozen:
> >> dev_warn(dev->ctrl.device,
> >> "frozen state error detected, reset controller\n");
> >> - if (!nvme_change_ctrl_state(&dev->ctrl, NVME_CTRL_RESETTING)) {
> >> - nvme_dev_disable(dev, true);
> >> - return PCI_ERS_RESULT_DISCONNECT;
> >> + if (nvme_ctrl_state(&dev->ctrl) != NVME_CTRL_RESETTING) {
> >> + if (!nvme_change_ctrl_state(&dev->ctrl, NVME_CTRL_RESETTING)) {
> >> + nvme_dev_disable(dev, true);
> >> + return PCI_ERS_RESULT_DISCONNECT;
> >> + }
> >> }
> >> nvme_dev_disable(dev, false);
> >> return PCI_ERS_RESULT_NEED_RESET;
> >
> > I get what you're trying to do, but it looks racy. The reset_work may
> > finish before pci sets channel offline, or the error handling work
> > happens to see RESETTING state, but then transitions to CONNECTING state
> > after and deadlocks on the '.resume()' side. You are counting on a very
> > specific sequence tied to the PCIe error handling module, and maybe you
> > are able to count on that sequence for your platform in this unique
> > scenario, but these link errors could happen anytime.
> >
> I am not sure about the deadlock in '.resume()' side you mentioned above.
> Did you mean that deadlock occur due to someone holding this pci_dev's device lock?
> Or deadlock occur due to the flush_work() from nvme_error_resume() would never
> return?

Your patch may observe a ctrl in "RESETTING" state from
error_detected(), then disable the controller, which quiesces the admin
queue. Meanwhile, reset_work may proceed to CONNECTING state and try
nvme_submit_sync_cmd(), which blocks forever because no one is going to
unquiesce that admin queue.