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Wed, 08 Apr 2020 08:24:39 -0700 (PDT) Received: from xz-x1 ([2607:9880:19c0:32::3]) by smtp.gmail.com with ESMTPSA id o67sm7628108wmo.5.2020.04.08.08.24.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 08 Apr 2020 08:24:38 -0700 (PDT) Date: Wed, 8 Apr 2020 11:24:35 -0400 From: Peter Xu To: Michal Hocko Cc: linux-kernel@vger.kernel.org, Linus Torvalds , linux-mm@kvack.org, Andrew Morton , syzbot+693dc11fcb53120b5559@syzkaller.appspotmail.com Subject: Re: [PATCH 1/2] mm/mempolicy: Allow lookup_node() to handle fatal signal Message-ID: <20200408152435.GH66033@xz-x1> References: <20200408014010.80428-1-peterx@redhat.com> <20200408014010.80428-2-peterx@redhat.com> <20200408102128.GX18914@dhcp22.suse.cz> <20200408142039.GD66033@xz-x1> <20200408143024.GZ18914@dhcp22.suse.cz> MIME-Version: 1.0 In-Reply-To: <20200408143024.GZ18914@dhcp22.suse.cz> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline 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 Wed, Apr 08, 2020 at 04:30:24PM +0200, Michal Hocko wrote: > On Wed 08-04-20 10:20:39, Peter Xu wrote: > > On Wed, Apr 08, 2020 at 12:21:28PM +0200, Michal Hocko wrote: > > > On Tue 07-04-20 21:40:09, Peter Xu wrote: > > > > lookup_node() uses gup to pin the page and get node information. I= t > > > > checks against ret>=3D0 assuming the page will be filled in. Howev= er > > > > it's also possible that gup will return zero, for example, when the > > > > thread is quickly killed with a fatal signal. Teach lookup_node() = to > > > > gracefully return an error -EFAULT if it happens. > > > >=20 > > > > Meanwhile, initialize "page" to NULL to avoid potential risk of > > > > exploiting the pointer. > > > >=20 > > > > Reported-by: syzbot+693dc11fcb53120b5559@syzkaller.appspotmail.com > > > > Fixes: 4426e945df58 ("mm/gup: allow VM_FAULT_RETRY for multiple tim= es") > > >=20 > > > I am not familiar with thic commit but shouldn't gup return ERESTARTS= YS > > > on a fatal signal? > >=20 > > Hi, Michal, > >=20 > > I do see quite a few usages on -ERESTARTSYS, but also some others, > > majorly -EINTR, or even -EFAULT. I think it could be a more general > > question rather than a specific question to this patch only. >=20 > I am sorry but I was probably not clear enough. I was mostly worried > that gup doesn't return ERESTARTSYS or EINTR when it backed off because > of fatal signal pending. Your patch is checking for 0 an indicating that > this is that condition. Yeah I just noticed the fact, sorry! Hillf just posted a fix there for recovering the behavior: https://lore.kernel.org/lkml/20200408151213.GE66033@xz-x1/ Thanks, --=20 Peter Xu