On Fri, Aug 16, 2019 at 08:20:55AM +0200, Daniel Vetter wrote: > On Fri, Aug 16, 2019 at 3:00 AM Jason Gunthorpe <jgg@xxxxxxxx> wrote: > > On Thu, Aug 15, 2019 at 10:49:31PM +0200, Daniel Vetter wrote: > > > On Thu, Aug 15, 2019 at 10:27 PM Jason Gunthorpe <jgg@xxxxxxxx> wrote: > > > > On Thu, Aug 15, 2019 at 10:16:43PM +0200, Daniel Vetter wrote: > > > > > So if someone can explain to me how that works with lockdep I can of > > > > > course implement it. But afaics that doesn't exist (I tried to explain > > > > > that somewhere else already), and I'm no really looking forward to > > > > > hacking also on lockdep for this little series. > > > > > > > > Hmm, kind of looks like it is done by calling preempt_disable() > > > > > > Yup. That was v1, then came the suggestion that disabling preemption > > > is maybe not the best thing (the oom reaper could still run for a long > > > time comparatively, if it's cleaning out gigabytes of process memory > > > or what not, hence this dedicated debug infrastructure). > > > > Oh, I'm coming in late, sorry > > > > Anyhow, I was thinking since we agreed this can trigger on some > > CONFIG_DEBUG flag, something like > > > > /* This is a sleepable region, but use preempt_disable to get debugging > > * for calls that are not allowed to block for OOM [.. insert > > * Michal's explanation.. ] */ > > if (IS_ENABLED(CONFIG_DEBUG_ATOMIC_SLEEP) && !mmu_notifier_range_blockable(range)) > > preempt_disable(); > > ops->invalidate_range_start(); > > I think we also discussed that, and some expressed concerns it would > change behaviour/timing too much for testing. Since this does does > disable preemption for real, not just for might_sleep. I don't follow, this is a debug kernel, it will have widly different timing. Further the point of this debugging on atomic_sleep is to be as timing-independent as possible since functions with rare sleeps should be guarded by might_sleep() in their common paths. I guess I don't get the push to have some low overhead debugging for this? Is there something special you are looking for? Jason
