On Jun 14, 2022 / 02:38, Chaitanya Kulkarni wrote: > Shinichiro, > > On 6/13/22 19:23, Keith Busch wrote: > > On Tue, Jun 14, 2022 at 01:09:07AM +0000, Shinichiro Kawasaki wrote: > >> (CC+: linux-pci) > >> On Jun 11, 2022 / 16:34, Yi Zhang wrote: > >>> On Fri, Jun 10, 2022 at 10:49 PM Keith Busch <kbusch@xxxxxxxxxx> wrote: > >>>> > >>>> And I am not even sure this is real. I don't know yet why this is showing up > >>>> only now, but this should fix it: > >>> > >>> Hi Keith > >>> > >>> Confirmed the WARNING issue was fixed with the change, here is the log: > >> > >> Thanks. I also confirmed that Keith's change to add __ATTR_IGNORE_LOCKDEP to > >> dev_attr_dev_rescan avoids the fix, on v5.19-rc2. > >> > >> I took a closer look into this issue and found The deadlock WARN can be > >> recreated with following two commands: > >> > >> # echo 1 > /sys/bus/pci/devices/0000\:00\:09.0/rescan > >> # echo 1 > /sys/bus/pci/devices/0000\:00\:09.0/remove > >> > >> And it can be recreated with PCI devices other than NVME controller, such as > >> SCSI controller or VGA controller. Then this is not a storage sub-system issue. > >> > >> I checked function call stacks of the two commands above. As shown below, it > >> looks like ABBA deadlock possibility is detected and warned. > > > > Yeah, I was mistaken on this report, so my proposal to suppress the warning is > > definitely not right. If I run both 'echo' commands in parallel, I see it > > deadlock frequently. I'm not familiar enough with this code to any good ideas > > on how to fix, but I agree this is a generic pci issue. > > I think it is worth adding a testcase to blktests to make sure these > future releases will test this. Yeah, this WARN is confusing for us then it would be valuable to test by blktests not to repeat it. One point I wonder is: which test group the test case will it fall in? The nvme group could be the group to add, probably. Another point I wonder is other kernel test suite than blktests. Don't we have more appropriate test suite to check PCI device rescan/remove race ? Such a test sounds more like a PCI bus sub-system test than block/storage test. Having said that, still I think the test case is valuable for block/storage. Unless anyone opposes, I'm open for the patch to add it. -- Shin'ichiro Kawasaki
