From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jerome Glisse Subject: Re: [PATCH 1/4] mm: Check if mmu notifier callbacks are allowed to fail Date: Tue, 21 May 2019 11:44:11 -0400 Message-ID: <20190521154411.GD3836@redhat.com> References: <20190520213945.17046-1-daniel.vetter@ffwll.ch> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Return-path: Content-Disposition: inline In-Reply-To: <20190520213945.17046-1-daniel.vetter@ffwll.ch> Sender: linux-kernel-owner@vger.kernel.org To: Daniel Vetter Cc: DRI Development , Intel Graphics Development , LKML , Linux MM , Andrew Morton , Michal Hocko , Christian =?iso-8859-1?Q?K=F6nig?= , David Rientjes , Paolo Bonzini , Daniel Vetter List-Id: dri-devel@lists.freedesktop.org On Mon, May 20, 2019 at 11:39:42PM +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. > > Cc: Andrew Morton > Cc: Michal Hocko > Cc: "Christian König" > Cc: David Rientjes > Cc: Daniel Vetter > Cc: "Jérôme Glisse" > Cc: linux-mm@kvack.org > Cc: Paolo Bonzini > Reviewed-by: Christian König > Signed-off-by: Daniel Vetter Reviewed-by: Jérôme Glisse > --- > mm/mmu_notifier.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c > index ee36068077b6..c05e406a7cd7 100644 > --- a/mm/mmu_notifier.c > +++ b/mm/mmu_notifier.c > @@ -181,6 +181,9 @@ int __mmu_notifier_invalidate_range_start(struct mmu_notifier_range *range) > pr_info("%pS callback failed with %d in %sblockable context.\n", > mn->ops->invalidate_range_start, _ret, > !mmu_notifier_range_blockable(range) ? "non-" : ""); > + if (!mmu_notifier_range_blockable(range)) > + pr_warn("%pS callback failure not allowed\n", > + mn->ops->invalidate_range_start); > ret = _ret; > } > } > -- > 2.20.1 >