From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752796AbeDXR2z (ORCPT ); Tue, 24 Apr 2018 13:28:55 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:56794 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751061AbeDXR2v (ORCPT ); Tue, 24 Apr 2018 13:28:51 -0400 Date: Tue, 24 Apr 2018 13:28:49 -0400 (EDT) From: Mikulas Patocka X-X-Sender: mpatocka@file01.intranet.prod.int.rdu2.redhat.com To: Michal Hocko cc: Matthew Wilcox , David Miller , Andrew Morton , linux-mm@kvack.org, eric.dumazet@gmail.com, edumazet@google.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, mst@redhat.com, jasowang@redhat.com, virtualization@lists.linux-foundation.org, dm-devel@redhat.com, Vlastimil Babka Subject: Re: [PATCH v3] kvmalloc: always use vmalloc if CONFIG_DEBUG_SG In-Reply-To: <20180424170349.GQ17484@dhcp22.suse.cz> Message-ID: References: <20180420210200.GH10788@bombadil.infradead.org> <20180421144757.GC14610@bombadil.infradead.org> <20180423151545.GU17484@dhcp22.suse.cz> <20180424125121.GA17484@dhcp22.suse.cz> <20180424162906.GM17484@dhcp22.suse.cz> <20180424170349.GQ17484@dhcp22.suse.cz> User-Agent: Alpine 2.02 (LRH 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 24 Apr 2018, Michal Hocko wrote: > On Tue 24-04-18 13:00:11, Mikulas Patocka wrote: > > > > > > On Tue, 24 Apr 2018, Michal Hocko wrote: > > > > > On Tue 24-04-18 11:50:30, Mikulas Patocka wrote: > > > > > > > > > > > > On Tue, 24 Apr 2018, Michal Hocko wrote: > > > > > > > > > On Mon 23-04-18 20:06:16, Mikulas Patocka wrote: > > > > > [...] > > > > > > @@ -404,6 +405,12 @@ void *kvmalloc_node(size_t size, gfp_t f > > > > > > */ > > > > > > WARN_ON_ONCE((flags & GFP_KERNEL) != GFP_KERNEL); > > > > > > > > > > > > +#ifdef CONFIG_DEBUG_SG > > > > > > + /* Catch bugs when the caller uses DMA API on the result of kvmalloc. */ > > > > > > + if (!(prandom_u32_max(2) & 1)) > > > > > > + goto do_vmalloc; > > > > > > +#endif > > > > > > > > > > I really do not think there is anything DEBUG_SG specific here. Why you > > > > > simply do not follow should_failslab path or even reuse the function? > > > > > > > > CONFIG_DEBUG_SG is enabled by default in RHEL and Fedora debug kernel (if > > > > you don't like CONFIG_DEBUG_SG, pick any other option that is enabled > > > > there). > > > > > > Are you telling me that you are shaping a debugging functionality basing > > > on what RHEL has enabled? And you call me evil. This is just rediculous. > > > > > > > Fail-injection framework is if off by default and it must be explicitly > > > > enabled and configured by the user - and most users won't enable it. > > > > > > It can be enabled easily. And if you care enough for your debugging > > > kernel then just make it enabled unconditionally. > > > > So, should we add a new option CONFIG_KVMALLOC_FALLBACK_DEFAULT? I'm not > > quite sure if 3 lines of debugging code need an extra option, but if you > > don't want to reuse any existing debug option, it may be possible. Adding > > it to the RHEL debug kernel would be trivial. > > Wouldn't it be equally trivial to simply enable the fault injection? You > would get additional failure paths testing as a bonus. The RHEL and Fedora debugging kernels are compiled with fault injection. But the fault-injection framework will do nothing unless it is enabled by a kernel parameter or debugfs write. Most users don't know about the fault injection kernel parameters or debugfs files and won't enabled it. We need a CONFIG_ option to enable it by default in the debugging kernels (and we could add a kernel parameter to override the default, fine-tune the fallback probability etc.) Mikulas