On Wed, Dec 18, 2024 at 03:26:38PM +0100, Johan Hovold wrote: > On Wed, Dec 18, 2024 at 07:39:10PM +0530, Manivannan Sadhasivam wrote: > > On Wed, Dec 18, 2024 at 02:55:02PM +0100, Johan Hovold wrote: > > > On Wed, Dec 18, 2024 at 06:00:19PM +0530, Manivannan Sadhasivam wrote: > > > > On Wed, Dec 18, 2024 at 01:02:39PM +0100, Johan Hovold wrote: > > > > > On Wed, Dec 18, 2024 at 05:08:30PM +0530, Manivannan Sadhasivam wrote: > > > > > > On Wed, Dec 18, 2024 at 09:40:45AM +0100, Johan Hovold wrote: > > > > > > > > > > > > I've tracked down the hang to a deadlock on the parent device lock. > > > > > > > > > > > > > > Driver core takes the parent device lock before calling shutdown(), and > > > > > > > then mhi_pci_shutdown() waits indefinitely for the recovery thread to > > > > > > > finish. > > > > > > > > > > > Thanks for tracking the deadlock. I think we should use pci_try_reset_function() > > > > > > instead of pci_reset_function() in mhi_pci_recovery_work(). > > > > > > > > > > > > If the pci_dev_lock() is already taken, it will return with -EAGAIN and we do > > > > > > not need to worry in that case since the host is going to be powered off anyway > > > > > > (and so the device). > > > > > > > > > > That may work. But note that I've now also seen this deadlock during > > > > > suspend (i.e. when the device is not going away). The > > > > > pci_try_reset_function() should avoid the deadlock here too, but we'll > > > > > end up in funny state. > > > > > > > > Hopefully, recovery_work() started by mhi_pci_runtime_resume() would be able to > > > > reset the device. > > > > > > But that's not going to happen as that reset is what is currently > > > causing the deadlock and which would simply be skipped if you switch to > > > pci_try_reset_function(). > > > > > > > mhi_pci_runtime_resume() will queue the recovery_work() and return. So I was > > hoping that by the time pci_try_reset_function() is called, the lock would be > > available. > > We can't rely on luck with timings, and this is the very reason for the > deadlock I'm currently seeing (i.e. the recovery thread is still running > when another thread grabs the lock and waits for the recovery thread to > finish). > > Perhaps the recovery work should be done synchronously in the resume > handler to avoid such issues. > Synchronously? How can that help when the recovery_work() cannot acquire the lock? Anyhow, even if the lock is not available during resume (worst case), PCI core should reset the device when it tries to change the state. I don't know if there is any better solution available. - Mani -- மணிவண்ணன் சதாசிவம்
