On Mon 20-09-21 15:29:46, Sultan Alsawaf wrote: > On Mon, Sep 20, 2021 at 10:30:12PM +0200, Michal Hocko wrote: > > We usually tend to provide Fixes where there has been something fixed. > > It seems just confusing if it is used for non functional changes, > > cleanups etc. Thera are gray zones of course. > > Got it, thanks. So no tag would be used in such a case? > > > I am not sure I follow. My understanding is that we need to make sure > > oom_reaper is not running after the quiescent state as it is changing > > user space address space. For that I believe we need to freeze the > > kthread at a proper moment. That is currently the entry point and maybe > > we can extend that even to the reaping loop but I haven't really > > explored that. PF_FREEZER_SKIP would skip over the reaper and that could > > result in it racing with the snapshotting no? > > Kthreads cannot be implicitly frozen; it's not like PREEMPT. From what I've read > in the freezer code, two things must occur for a kthread to freeze: the kthread > must have PF_NOFREEZE unset (via set_freezable(), as is done in the patch I've > submitted here), and the kthread must have an explicit call into the freezer, > such as via wait_event_freezable(). > > Right now, oom_reaper is totally ignored by the freezer because PF_NOFREEZE is > set by default in all kthreads. As such, oom_reaper can keep running while > system-wide freezing occurs. If you think this can mangle snapshots, then > perhaps there is a real bug here after all. OK, now I am getting your point. Sorry for being dense here. Process freezing has always been kinda muddy to me as I've said earlier. I have completely misunderstood your earlier PF_NOFREEZE remark. -- Michal Hocko SUSE Labs
