From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 28C19C43334 for ; Wed, 8 Jun 2022 03:28:16 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 83DA36B0071; Tue, 7 Jun 2022 23:28:15 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 7EBB76B0072; Tue, 7 Jun 2022 23:28:15 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6B3796B0073; Tue, 7 Jun 2022 23:28:15 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id 5A0CF6B0071 for ; Tue, 7 Jun 2022 23:28:15 -0400 (EDT) Received: from smtpin22.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 2949160F3D for ; Wed, 8 Jun 2022 03:28:15 +0000 (UTC) X-FDA: 79553635350.22.66832BB Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf08.hostedemail.com (Postfix) with ESMTP id 4562A16004A for ; Wed, 8 Jun 2022 03:28:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=rb8PtiqYu5cbp4L1/wbvkrZWp96775LgK31d20avxd0=; b=XDQVraJG6VNU51qlL2Cm9Ls3AW QwUxqU1rbHT7aux/Hf7mU8uBRW+nAvn/g434eK7KcdQvxHq1XqCkXN45g0Jy0uDMpBxtcUzRZ8JYb L9o9w1mjqa/kbQBQism8A7rfvU4zaxYSQVB0bLTNhZo2xNHD4NxtmLg/wNo766JpC75Lj2PXd/HJ1 Yu1kWx7yGd6y/F7zAVvZ2sfYrAhImlz+3cG82JXuajyGx23L1xPDzBWasTjfmgUnEycNQIzdZBJ6L LRFZoUyM5iBpbcBtzAwxgjseaIER0sY7FETYccxpTBBLQskNFCTPh9rXB6RUZ+1y5o1C8fbDFcPcN qQbhKTUg==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1nymJw-00CH9N-Dj; Wed, 08 Jun 2022 03:25:24 +0000 Date: Wed, 8 Jun 2022 04:25:24 +0100 From: Matthew Wilcox To: Dmitry Vyukov Cc: Dan Carpenter , Greg KH , Alan Stern , Andy Shevchenko , syzbot , hdanton@sina.com, lenb@kernel.org, linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org, rafael.j.wysocki@intel.com, rafael@kernel.org, rjw@rjwysocki.net, syzkaller-bugs@googlegroups.com, linux-usb@vger.kernel.org, Linux-MM Subject: Re: [syzbot] general protection fault in __device_attach Message-ID: References: <000000000000bb7f1c05da29b601@google.com> <00000000000010b7d305e08837c8@google.com> <20220606123839.GW2146@kadam> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: Authentication-Results: imf08.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=XDQVraJG; dmarc=none; spf=none (imf08.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 4562A16004A X-Stat-Signature: 51uxc4buytb3j7a79ggo8jbo9pgkdd66 X-HE-Tag: 1654658893-465647 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 Tue, Jun 07, 2022 at 09:15:09AM +0200, Dmitry Vyukov wrote: > On Mon, 6 Jun 2022 at 14:39, Dan Carpenter wrote: > > > > On Sat, Jun 04, 2022 at 10:32:46AM +0200, 'Dmitry Vyukov' via syzkaller-bugs wrote: > > > On Fri, 3 Jun 2022 at 18:12, Greg KH wrote: > > > > > > > > But again, is this a "real and able to be triggered from userspace" > > > > problem, or just fault-injection-induced? > > > > > > Then this is something to fix in the fault injection subsystem. > > > Testing systems shouldn't be reporting false positives. > > > What allocations cannot fail in real life? Is it <=page_size? > > > > > > > Apparently in 2014, anything less than *EIGHT?!!* pages succeeded! > > > > https://lwn.net/Articles/627419/ > > > > I have been on the look out since that article and never seen anyone > > mention it changing. I think we should ignore that and say that > > anything over PAGE_SIZE can fail. Possibly we could go smaller than > > PAGE_SIZE... > > +linux-mm for GFP expertise re what allocations cannot possibly fail > and should be excluded from fault injection. > > Interesting, thanks for the link. > > PAGE_SIZE looks like a good start. Once we have the predicate in > place, we can refine it later when/if we have more inputs. > > But I wonder about GFP flags. They definitely have some impact on allocations. > If GFP_ACCOUNT is set, all allocations can fail, right? > If GFP_DMA/DMA32 is set, allocations can fail, right? What about other zones? > If GFP_NORETRY is set, allocations can fail? > What about GFP_NOMEMALLOC and GFP_ATOMIC? > What about GFP_IO/GFP_FS/GFP_DIRECT_RECLAIM/GFP_KSWAPD_RECLAIM? At > least some of these need to be set for allocations to not fail? Which > ones? > Any other flags are required to be set/unset for allocations to not fail? I'm not the expert on page allocation, but ... I don't think GFP_ACCOUNT makes allocations fail. It might make reclaim happen from within that cgroup, and it might cause an OOM kill for something in that cgroup. But I don't think it makes a (low order) allocation more likely to fail. There's usually less memory avilable in DMA/DMA32 zones, but we have so few allocations from those zones, I question the utility of focusing testing on those allocations. GFP_ATOMIC allows access to emergency pools, so I would say _less_ likely to fail. KSWAPD_RECLAIM has no effect on whether _this_ allocation succeeds or fails; it kicks kswapd to do reclaim, rather than doing reclaim directly. DIRECT_RECLAIM definitely makes allocations more likely to succeed. GFP_FS allows (direct) reclaim to happen from filesystems. GFP_IO allows IO to start (ie writeback can start) in order to clean dirty memory. Anyway, I hope somebody who knows the page allocator better than I do can say smarter things than this. Even better if they can put it into Documentation/ somewhere ;-) https://www.kernel.org/doc/html/latest/core-api/memory-allocation.html exists but isn't quite enough to answer this question.