On Tue, Aug 20, 2019 at 10:24:40PM +0200, Daniel Vetter wrote: > On Tue, Aug 20, 2019 at 10:19:01AM +0200, Daniel Vetter wrote: > > In some special cases we must not block, but there's not a > > spinlock, preempt-off, irqs-off or similar critical section already > > that arms the might_sleep() debug checks. Add a non_block_start/end() > > pair to annotate these. > > > > This will be used in the oom paths of mmu-notifiers, where blocking is > > not allowed to make sure there's forward progress. Quoting Michal: > > > > "The notifier is called from quite a restricted context - oom_reaper - > > which shouldn't depend on any locks or sleepable conditionals. The code > > should be swift as well but we mostly do care about it to make a forward > > progress. Checking for sleepable context is the best thing we could come > > up with that would describe these demands at least partially." > > > > Peter also asked whether we want to catch spinlocks on top, but Michal > > said those are less of a problem because spinlocks can't have an > > indirect dependency upon the page allocator and hence close the loop > > with the oom reaper. > > > > Suggested by Michal Hocko. > > > > v2: > > - Improve commit message (Michal) > > - Also check in schedule, not just might_sleep (Peter) > > > > v3: It works better when I actually squash in the fixup I had lying > > around :-/ > > > > v4: Pick the suggestion from Andrew Morton to give non_block_start/end > > some good kerneldoc comments. I added that other blocking calls like > > wait_event pose similar issues, since that's the other example we > > discussed. > > > > Cc: Jason Gunthorpe <j...@ziepe.ca> > > Cc: Peter Zijlstra <pet...@infradead.org> > > Cc: Ingo Molnar <mi...@redhat.com> > > Cc: Andrew Morton <a...@linux-foundation.org> > > Cc: Michal Hocko <mho...@suse.com> > > Cc: David Rientjes <rient...@google.com> > > Cc: "Christian König" <christian.koe...@amd.com> > > Cc: Daniel Vetter <daniel.vet...@ffwll.ch> > > Cc: "Jérôme Glisse" <jgli...@redhat.com> > > Cc: linux...@kvack.org > > Cc: Masahiro Yamada <yamada.masah...@socionext.com> > > Cc: Wei Wang <w...@google.com> > > Cc: Andy Shevchenko <andriy.shevche...@linux.intel.com> > > Cc: Thomas Gleixner <t...@linutronix.de> > > Cc: Jann Horn <ja...@google.com> > > Cc: Feng Tang <feng.t...@intel.com> > > Cc: Kees Cook <keesc...@chromium.org> > > Cc: Randy Dunlap <rdun...@infradead.org> > > Cc: linux-kernel@vger.kernel.org > > Acked-by: Christian König <christian.koe...@amd.com> (v1) > > Signed-off-by: Daniel Vetter <daniel.vet...@intel.com> > > Hi Peter, > > Iirc you've been involved at least somewhat in discussing this. -mm folks > are a bit undecided whether these new non_block semantics are a good idea. > Michal Hocko still is in support, but Andrew Morton and Jason Gunthorpe > are less enthusiastic. Jason said he's ok with merging the hmm side of > this if scheduler folks ack. If not, then I'll respin with the > preempt_disable/enable instead like in v1. > > So ack/nack for this from the scheduler side?
Right, I had memories of seeing this before, and I just found a fairly long discussion on this elsewhere in the vacation inbox (*groan*). Yeah, this is something I can live with, Acked-by: Peter Zijlstra (Intel) <pet...@infradead.org>
