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[156.34.55.100]) by smtp.gmail.com with ESMTPSA id t15sm2084806qtr.88.2019.08.15.18.00.36 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 15 Aug 2019 18:00:36 -0700 (PDT) Received: from jgg by mlx.ziepe.ca with local (Exim 4.90_1) (envelope-from ) id 1hyQbc-0002v2-3C; Thu, 15 Aug 2019 22:00:36 -0300 Date: Thu, 15 Aug 2019 22:00:36 -0300 From: Jason Gunthorpe To: Daniel Vetter Cc: Michal Hocko , Feng Tang , Randy Dunlap , Kees Cook , Masahiro Yamada , Peter Zijlstra , Intel Graphics Development , Jann Horn , LKML , DRI Development , Linux MM , =?utf-8?B?SsOpcsO0bWU=?= Glisse , Ingo Molnar , Thomas Gleixner , David Rientjes , Wei Wang , Daniel Vetter , Andrew Morton , Andy Shevchenko , Christian =?utf-8?B?S8O2bmln?= Subject: Re: [Intel-gfx] [PATCH 2/5] kernel.h: Add non_block_start/end() Message-ID: <20190816010036.GA9915@ziepe.ca> References: <20190815155950.GN9477@dhcp22.suse.cz> <20190815165631.GK21596@ziepe.ca> <20190815174207.GR9477@dhcp22.suse.cz> <20190815182448.GP21596@ziepe.ca> <20190815190525.GS9477@dhcp22.suse.cz> <20190815191810.GR21596@ziepe.ca> <20190815193526.GT9477@dhcp22.suse.cz> <20190815202721.GV21596@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 15, 2019 at 10:49:31PM +0200, Daniel Vetter wrote: > On Thu, Aug 15, 2019 at 10:27 PM Jason Gunthorpe wrote: > > On Thu, Aug 15, 2019 at 10:16:43PM +0200, Daniel Vetter wrote: > > > So if someone can explain to me how that works with lockdep I can of > > > course implement it. But afaics that doesn't exist (I tried to explain > > > that somewhere else already), and I'm no really looking forward to > > > hacking also on lockdep for this little series. > > > > Hmm, kind of looks like it is done by calling preempt_disable() > > Yup. That was v1, then came the suggestion that disabling preemption > is maybe not the best thing (the oom reaper could still run for a long > time comparatively, if it's cleaning out gigabytes of process memory > or what not, hence this dedicated debug infrastructure). Oh, I'm coming in late, sorry Anyhow, I was thinking since we agreed this can trigger on some CONFIG_DEBUG flag, something like /* This is a sleepable region, but use preempt_disable to get debugging * for calls that are not allowed to block for OOM [.. insert * Michal's explanation.. ] */ if (IS_ENABLED(CONFIG_DEBUG_ATOMIC_SLEEP) && !mmu_notifier_range_blockable(range)) preempt_disable(); ops->invalidate_range_start(); And I have also been idly mulling doing something like if (IS_ENABLED(CONFIG_DEBUG_NOTIFIERS) && rand && mmu_notifier_range_blockable(range)) { range->flags = 0 if (!ops->invalidate_range_start(range)) continue // Failed, try again as blockable range->flags = MMU_NOTIFIER_RANGE_BLOCKABLE } ops->invalidate_range_start(range); Which would give coverage for this corner case without forcing OOM. Jason