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[37.188.180.223]) by smtp.gmail.com with ESMTPSA id p7sm3142652wrf.31.2020.04.08.08.26.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 08 Apr 2020 08:26:32 -0700 (PDT) Date: Wed, 8 Apr 2020 17:26:30 +0200 From: Michal Hocko To: Peter Xu 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: <20200408152630.GA18914@dhcp22.suse.cz> 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> <20200408152435.GH66033@xz-x1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200408152435.GH66033@xz-x1> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 08-04-20 11:24:35, Peter Xu wrote: > 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. It > > > > > checks against ret>=0 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. > > > > > > > > > > Meanwhile, initialize "page" to NULL to avoid potential risk of > > > > > exploiting the pointer. > > > > > > > > > > Reported-by: syzbot+693dc11fcb53120b5559@syzkaller.appspotmail.com > > > > > Fixes: 4426e945df58 ("mm/gup: allow VM_FAULT_RETRY for multiple times") > > > > > > > > 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 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/ yeah, that is the proper fix. -- Michal Hocko SUSE Labs