On Wed, Aug 14, 2019 at 10:20:23PM +0200, Daniel Vetter wrote: > Just a bit of paranoia, since if we start pushing this deep into > callchains it's hard to spot all places where an mmu notifier > implementation might fail when it's not allowed to. > > Inspired by some confusion we had discussing i915 mmu notifiers and > whether we could use the newly-introduced return value to handle some > corner cases. Until we realized that these are only for when a task > has been killed by the oom reaper. > > An alternative approach would be to split the callback into two > versions, one with the int return value, and the other with void > return value like in older kernels. But that's a lot more churn for > fairly little gain I think. > > Summary from the m-l discussion on why we want something at warning > level: This allows automated tooling in CI to catch bugs without > humans having to look at everything. If we just upgrade the existing > pr_info to a pr_warn, then we'll have false positives. And as-is, no > one will ever spot the problem since it's lost in the massive amounts > of overall dmesg noise. > > v2: Drop the full WARN_ON backtrace in favour of just a pr_warn for > the problematic case (Michal Hocko). > > v3: Rebase on top of Glisse's arg rework. > > v4: More rebase on top of Glisse reworking everything. > > v5: Fixup rebase damage and also catch failures != EAGAIN for > !blockable (Jason). Also go back to WARN_ON as requested by Jason, so > automatic checkers can easily catch bugs by setting panic_on_warn. > > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxxx> > Cc: "Christian König" <christian.koenig@xxxxxxx> > Cc: David Rientjes <rientjes@xxxxxxxxxx> > Cc: Daniel Vetter <daniel.vetter@xxxxxxxx> > Cc: "Jérôme Glisse" <jglisse@xxxxxxxxxx> > Cc: linux-mm@xxxxxxxxx > Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> > Cc: Jason Gunthorpe <jgg@xxxxxxxx> > Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx> > --- > mm/mmu_notifier.c | 2 ++ > 1 file changed, 2 insertions(+) Applied to hmm.git, thanks Jason
