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[209.132.183.28]) by mx.google.com with ESMTPS id n55si22898309qtf.56.2019.07.28.22.56.27 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 28 Jul 2019 22:56:27 -0700 (PDT) Received-SPF: pass (google.com: domain of jasowang@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of jasowang@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=jasowang@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 78B46308FC47; Mon, 29 Jul 2019 05:56:26 +0000 (UTC) Received: from [10.72.12.53] (ovpn-12-53.pek2.redhat.com [10.72.12.53]) by smtp.corp.redhat.com (Postfix) with ESMTP id 7C62660C5F; Mon, 29 Jul 2019 05:56:10 +0000 (UTC) Subject: Re: WARNING in __mmdrop To: Jason Gunthorpe 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 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> <20190726150322.GB8695@ziepe.ca> From: Jason Wang Message-ID: Date: Mon, 29 Jul 2019 13:56:08 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190726150322.GB8695@ziepe.ca> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.43]); Mon, 29 Jul 2019 05:56:26 +0000 (UTC) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2019/7/26 下午11:03, Jason Gunthorpe wrote: > 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. Yes, I get this. > > 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. Right, let me optimize that. Thanks > > Jason