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[37.188.180.223]) by smtp.gmail.com with ESMTPSA id q8sm250026wmg.22.2020.04.08.10.13.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 08 Apr 2020 10:13:13 -0700 (PDT) Date: Wed, 8 Apr 2020 19:13:10 +0200 From: Michal Hocko To: Linus Torvalds Cc: Peter Xu , Linux-MM , Linux Kernel Mailing List , Andrew Morton , Hillf Danton , Thomas Gleixner , Peter Zijlstra , syzbot+3be1a33f04dc782e9fd5@syzkaller.appspotmail.com Subject: Re: [PATCH] mm/gup: Let __get_user_pages_locked() return -EINTR for fatal signal Message-ID: <20200408171023.GC18914@dhcp22.suse.cz> References: <20200408155924.107722-1-peterx@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 08-04-20 09:20:00, Linus Torvalds wrote: > On Wed, Apr 8, 2020 at 8:59 AM Peter Xu wrote: > > > > __get_user_pages_locked() will return 0 instead of -EINTR after commit > > 4426e945df588 which added extra code to allow gup detect fatal signal > > faster. Restore that behavior. > > I've applied this, but it's worth noting that > __get_user_pages_locked() can still return 0 in other situations. > > I realize that "I got zero pages" is a valid return value, but I do > wonder if we should make the rule be that a zero return value isn't > possible (return -EAGAIN or whatever if you doin't have the > EFAULT/EINTR conditions). > > So that you'd always get either an error, or a successful number of pages. > > The only case where __get_user_pages_locked() might return zero is if > you pass in a zero 'nr_pages', although I suspect even for that case > returning -EINVAL might be a better option. Yeah, that makes sense to me. And get_user_pages_locked documentation would benefit from an actual documentation as well. What we have right now is more suited to the lower level (__get_user_pages_locked) and have a high level user oriented documentation. -- Michal Hocko SUSE Labs