On Tue, Apr 07, 2020 at 02:39:42PM +0200, Dmitry Vyukov wrote: > On Tue, Apr 7, 2020 at 1:55 PM Jason Gunthorpe <jgg@xxxxxxxx> wrote: > > > > On Tue, Apr 07, 2020 at 11:56:30AM +0200, Dmitry Vyukov wrote: > > > > I'm not sure what could be done wrong here to elicit this: > > > > > > > > sysfs group 'power' not found for kobject 'umad1' > > > > > > > > ?? > > > > > > > > I've seen another similar sysfs related trigger that we couldn't > > > > figure out. > > > > > > > > Hard to investigate without a reproducer. > > > > > > Based on all of the sysfs-related bugs I've seen, my bet would be on > > > some races. E.g. one thread registers devices, while another > > > unregisters these. > > > > I did check that the naming is ordered right, at least we won't be > > concurrently creating and destroying umadX sysfs of the same names. > > > > I'm also fairly sure we can't be destroying the parent at the same > > time as this child. > > > > Do you see the above commonly? Could it be some driver core thing? Or > > is it more likely something wrong in umad? > > Mmmm... I can't say, I am looking at some bugs very briefly. I've > noticed that sysfs comes up periodically (or was it some other similar > fs?). General observation is that code frequently assumes only the > happy scenario and only, say, a single administrator doing one thing > at a time, slowly and carefully, and it is not really hardened against > armies of monkeys. > But I did not look at code abstractions, bug patterns, contracts, etc. > > Greg KH may know better. Greg, as far as I remember you commented on > some of these reports along the lines of, for example, "the warning is > in sysfs code, but the bug is in the callers". Yes, that is correct.
