Re: [PATCH] blk-mq: Abort suspend when wakeup events are pending

[Ming Lei <ming.lei@redhat.com>]

On Tue, Dec 02, 2025 at 05:48:21PM +0800, Cong Zhang wrote:
> 
> 
> On 12/2/2025 5:20 PM, Ming Lei wrote:
> > On Tue, Dec 02, 2025 at 11:56:12AM +0800, Cong Zhang wrote:
> >> During system suspend, wakeup capable IRQs for block device can be
> >> delayed, which can cause blk_mq_hctx_notify_offline() to hang
> >> indefinitely while waiting for pending request to complete.
> >> Skip the request waiting loop and abort suspend when wakeup events are
> >> pending to prevent the deadlock.
> >>
> >> Fixes: bf0beec0607d ("blk-mq: drain I/O when all CPUs in a hctx are offline")
> >> Signed-off-by: Cong Zhang <cong.zhang@oss.qualcomm.com>
> >> ---
> >> The issue was found during system suspend with a no_soft_reset
> >> virtio-blk device. Here is the detailed analysis:
> >> - When system suspend starts and no_soft_reset is enabled, virtio-blk
> >>   does not call its suspend callback.
> >> - Some requests are dispatched and queued. After sending the virtqueue
> >>   notifier, the kernel waits for an IRQ to complete the request.
> >> - The virtio-blk IRQ is wakeup-capable. When the IRQ is triggered, it
> >>   remains pending because the device is in the suspend process.
> > 
> > Can you explain a bit for above point? Why does the IRQ remains pending
> > and not get handled?
> > 
> 
> The wakeup capable IRQ is not masked during suspend. When the IRQ is
> triggered, the kernel does not call its IRQ handler, instead kernel only
> marks the IRQ as a wakeup event in pm_system_irq_wakeup(). By checking
> pm_wakeup_pending() suspend process can abort if a wakeup event is
> detected. That means the actual IRQ handler is not called during the
> checking of blk_mq_hctx_has_requests, which cause the issue.

Thanks for the explanation!

Can you document it around `if (pm_wakeup_pending)`?

Otherwise, this patch looks fine for me.


Thanks,
Ming