From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f198.google.com (mail-wr0-f198.google.com [209.85.128.198]) by kanga.kvack.org (Postfix) with ESMTP id 3CBF76B0006 for ; Tue, 24 Apr 2018 13:03:54 -0400 (EDT) Received: by mail-wr0-f198.google.com with SMTP id f23-v6so18311720wra.20 for ; Tue, 24 Apr 2018 10:03:54 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id 46si992573edu.103.2018.04.24.10.03.53 for (version=TLS1 cipher=AES128-SHA bits=128/128); Tue, 24 Apr 2018 10:03:53 -0700 (PDT) Date: Tue, 24 Apr 2018 11:03:49 -0600 From: Michal Hocko Subject: Re: [PATCH v3] kvmalloc: always use vmalloc if CONFIG_DEBUG_SG Message-ID: <20180424170349.GQ17484@dhcp22.suse.cz> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Mikulas Patocka 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 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. -- Michal Hocko SUSE Labs