On Fri, Aug 02, 2019 at 04:23:33PM +0800, Xiongfeng Wang wrote: > If I use a global flag to mark if any pci device is being rescaned or > removed, the problem is that we can't remove two devices belonging to > two root ports at the same time. > Since a root port produces a pci tree, so I was planning to make the > flag per root port slot. I mean add the flag in 'struct slot'. > But in some situation, the root port doesn't support hotplug and the > downport below the root port support hotplug. I am not sure if it's > better to add the flag in 'struct pci_dev' of the root port. We're susceptible to deadlocks if at least two hotplug ports are removed simultaneously where one is a parent of the other. What you're witnessing is basically a variation of that problem wherein a hotplug port is removed while it is simultaneously removing its children. pci_lock_rescan_remove(), which was introduced by commit 9d16947b7583 to fix races (which are real), at the same time caused these deadlocks. The lock is too coarse-grained and needs to be replaced with more fine-grained locking. Specifically, unbinding PCI devices from drivers on removal need not and should not happen under that lock. That will fix all the deadlocks. I've submitted a patch last year to address one class of those deadlocks but withdrew it as I realized it's not a proper fix: https://patchwork.kernel.org/patch/10468065/ What you can do is add a flag to struct pci_dev (or the priv_flags embedded therein) to indicate that a device is about to be removed. Set this flag on all children of the device being removed before acquiring pci_lock_rescan_remove() and avoid taking that lock in pciehp_unconfigure_device() if the flag is set on the hotplug port. But again, that approach is just a band-aid and the real fix is to unbind devices without holding the lock. Thanks, Lukas
