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Wed, 08 Apr 2020 07:20:43 -0700 (PDT) Received: from xz-x1 ([2607:9880:19c0:32::3]) by smtp.gmail.com with ESMTPSA id u6sm29411783wrm.65.2020.04.08.07.20.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 08 Apr 2020 07:20:42 -0700 (PDT) Date: Wed, 8 Apr 2020 10:20:39 -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: <20200408142039.GD66033@xz-x1> References: <20200408014010.80428-1-peterx@redhat.com> <20200408014010.80428-2-peterx@redhat.com> <20200408102128.GX18914@dhcp22.suse.cz> MIME-Version: 1.0 In-Reply-To: <20200408102128.GX18914@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 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. It > > checks against ret>=3D0 assuming the page will be filled in. However > > 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 times") >=20 > I am not familiar with thic commit but shouldn't gup return ERESTARTSYS > on a fatal signal? Hi, Michal, 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. I saw some other discussions about this return value issue, I'll CC you in the other thread when I raise this as a general question. Thanks, --=20 Peter Xu