On Wed, 14 Mar 2018 15:09:09 -0700 Tejun Heo <tj@xxxxxxxxxx> wrote: > Hello, Andrew. > > On Wed, Mar 14, 2018 at 01:56:31PM -0700, Andrew Morton wrote: > > It would benefit from a comment explaining why we're doing this (it's > > for the oom-killer). > > Will add. > > > My memory is weak and our documentation is awful. What does > > mutex_lock_killable() actually do and how does it differ from > > mutex_lock_interruptible()? Userspace tasks can run pcpu_alloc() and I > > IIRC, killable listens only to SIGKILL. > > > wonder if there's any way in which a userspace-delivered signal can > > disrupt another userspace task's memory allocation attempt? > > Hmm... maybe. Just honoring SIGKILL *should* be fine but the alloc > failure paths might be broken, so there are some risks. Given that > the cases where userspace tasks end up allocation percpu memory is > pretty limited and/or priviledged (like mount, bpf), I don't think the > risks are high tho. hm. spose so. Maybe. Are there other ways? I assume the time is being spent in pcpu_create_chunk()? We could drop the mutex while running that stuff and take the appropriate did-we-race-with-someone testing after retaking it. Or similar.
