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[156.34.55.100]) by smtp.gmail.com with ESMTPSA id u71sm25391649qka.21.2019.07.26.08.03.23 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 26 Jul 2019 08:03:24 -0700 (PDT) Received: from jgg by mlx.ziepe.ca with local (Exim 4.90_1) (envelope-from ) id 1hr1kg-0000d9-RM; Fri, 26 Jul 2019 12:03:22 -0300 Date: Fri, 26 Jul 2019 12:03:22 -0300 From: Jason Gunthorpe To: Jason Wang Cc: "Michael S. Tsirkin" , syzbot , aarcange@redhat.com, akpm@linux-foundation.org, christian@brauner.io, davem@davemloft.net, ebiederm@xmission.com, elena.reshetova@intel.com, guro@fb.com, hch@infradead.org, james.bottomley@hansenpartnership.com, jglisse@redhat.com, keescook@chromium.org, ldv@altlinux.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-parisc@vger.kernel.org, luto@amacapital.net, mhocko@suse.com, mingo@kernel.org, namit@vmware.com, peterz@infradead.org, syzkaller-bugs@googlegroups.com, viro@zeniv.linux.org.uk, wad@chromium.org Subject: Re: WARNING in __mmdrop Message-ID: <20190726150322.GB8695@ziepe.ca> References: <20190725042651-mutt-send-email-mst@kernel.org> <84bb2e31-0606-adff-cf2a-e1878225a847@redhat.com> <20190725092332-mutt-send-email-mst@kernel.org> <11802a8a-ce41-f427-63d5-b6a4cf96bb3f@redhat.com> <20190726074644-mutt-send-email-mst@kernel.org> <5cc94f15-b229-a290-55f3-8295266edb2b@redhat.com> <20190726082837-mutt-send-email-mst@kernel.org> <20190726094353-mutt-send-email-mst@kernel.org> <63754251-a39a-1e0e-952d-658102682094@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <63754251-a39a-1e0e-952d-658102682094@redhat.com> 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 Fri, Jul 26, 2019 at 10:00:20PM +0800, Jason Wang wrote: > The question is, MMU notifier are allowed to be blocked on > invalidate_range_start() which could be much slower than synchronize_rcu() > to finish. > > Looking at amdgpu_mn_invalidate_range_start_gfx() which calls > amdgpu_mn_invalidate_node() which did: > >                 r = reservation_object_wait_timeout_rcu(bo->tbo.resv, >                         true, false, MAX_SCHEDULE_TIMEOUT); > > ... The general guidance has been that invalidate_start should block minimally, if at all. I would say synchronize_rcu is outside that guidance. BTW, always returning EAGAIN for mmu_notifier_range_blockable() is not good either, it should instead only return EAGAIN if any vhost_map_range_overlap() is true. Jason