From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ua0-f198.google.com (mail-ua0-f198.google.com [209.85.217.198]) by kanga.kvack.org (Postfix) with ESMTP id D9F886B0005 for ; Wed, 2 May 2018 09:33:03 -0400 (EDT) Received: by mail-ua0-f198.google.com with SMTP id b38so13195291uad.23 for ; Wed, 02 May 2018 06:33:03 -0700 (PDT) Received: from mx1.redhat.com (mx3-rdu2.redhat.com. [66.187.233.73]) by mx.google.com with ESMTPS id r41si1881074uai.59.2018.05.02.06.33.02 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 02 May 2018 06:33:02 -0700 (PDT) Date: Wed, 2 May 2018 09:33:01 -0400 From: Mike Snitzer Subject: Re: kvmalloc: always use vmalloc if CONFIG_DEBUG_VM Message-ID: <20180502133224.GA22123@redhat.com> References: <20180421144757.GC14610@bombadil.infradead.org> <20180423151545.GU17484@dhcp22.suse.cz> <20180424133146.GG17484@dhcp22.suse.cz> <20180424161242.GK17484@dhcp22.suse.cz> <20180501173626.4593a87d0d64f6cc9d219d20@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180501173626.4593a87d0d64f6cc9d219d20@linux-foundation.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Mikulas Patocka , dm-devel@redhat.com, eric.dumazet@gmail.com, mst@redhat.com, netdev@vger.kernel.org, jasowang@redhat.com, linux-kernel@vger.kernel.org, Matthew Wilcox , Michal Hocko , linux-mm@kvack.org, edumazet@google.com, Babka , virtualization@lists.linux-foundation.org, David Miller On Tue, May 01 2018 at 8:36pm -0400, Andrew Morton wrote: > On Tue, 24 Apr 2018 12:33:01 -0400 (EDT) Mikulas Patocka wrote: > > > > > > > On Tue, 24 Apr 2018, Michal Hocko wrote: > > > > > On Tue 24-04-18 11:30:40, Mikulas Patocka wrote: > > > > > > > > > > > > On Tue, 24 Apr 2018, Michal Hocko wrote: > > > > > > > > > On Mon 23-04-18 20:25:15, Mikulas Patocka wrote: > > > > > > > > > > > Fixing __vmalloc code > > > > > > is easy and it doesn't require cooperation with maintainers. > > > > > > > > > > But it is a hack against the intention of the scope api. > > > > > > > > It is not! > > > > > > This discussion simply doesn't make much sense it seems. The scope API > > > is to document the scope of the reclaim recursion critical section. That > > > certainly is not a utility function like vmalloc. > > > > That 15-line __vmalloc bugfix doesn't prevent you (or any other kernel > > developer) from converting the code to the scope API. You make nonsensical > > excuses. > > > > Fun thread! > > Winding back to the original problem, I'd state it as > > - Caller uses kvmalloc() but passes the address into vmalloc-naive > DMA API and > > - Caller uses kvmalloc() but passes the address into kfree() > > Yes? I think so. > If so, then... > > Is there a way in which, in the kvmalloc-called-kmalloc path, we can > tag the slab-allocated memory with a "this memory was allocated with > kvmalloc()" flag? I *think* there's extra per-object storage available > with suitable slab/slub debugging options? Perhaps we could steal one > bit from the redzone, dunno. > > If so then we can > > a) set that flag in kvmalloc() if the kmalloc() call succeeded > > b) check for that flag in the DMA code, WARN if it is set. > > c) in kvfree(), clear that flag before calling kfree() > > d) in kfree(), check for that flag and go WARN() if set. > > So both potential bugs are detected all the time, dependent upon > CONFIG_SLUB_DEBUG (and perhaps other slub config options). Thanks Andrew, definitely the most sane proposal I've seen to resolve this.