Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Tue, 9 Apr 2019 09:41:47 +1000
From:   "Tobin C. Harding" <me@tobin.cc>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Qian Cai <cai@lca.pw>, Andrew Morton <akpm@linux-foundation.org>,
        Christoph Lameter <cl@linux.com>, penberg@kernel.org,
        David Rientjes <rientjes@google.com>, iamjoonsoo.kim@lge.com,
        Tejun Heo <tj@kernel.org>, Linux-MM <linux-mm@kvack.org>,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] slab: fix a crash by reading /proc/slab_allocators
Message-ID: <20190408234147.GA14359@eros.localdomain>
References: <20190406225901.35465-1-cai@lca.pw>
 <CAHk-=wgr5ZYM3b4Sn9AwnJkiDNeHcW6qLY1Aha3VGT3pPih+WQ@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAHk-=wgr5ZYM3b4Sn9AwnJkiDNeHcW6qLY1Aha3VGT3pPih+WQ@mail.gmail.com>
User-Agent: Mutt/1.11.4 (2019-03-13)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Sun, Apr 07, 2019 at 07:35:34PM -1000, Linus Torvalds wrote:
> On Sat, Apr 6, 2019 at 12:59 PM Qian Cai <cai@lca.pw> wrote:
> >
> > The commit 510ded33e075 ("slab: implement slab_root_caches list")
> > changes the name of the list node within "struct kmem_cache" from
> > "list" to "root_caches_node", but leaks_show() still use the "list"
> > which causes a crash when reading /proc/slab_allocators.
> 
> The patch does seem to be correct, and I have applied it.
> 
> However, it does strike me that apparently this wasn't caught for two
> years. Which makes me wonder whether we should (once again) discuss
> just removing SLAB entirely, or at least removing the
> /proc/slab_allocators file. Apparently it has never been used in the
> last two years. At some point a "this can't have worked if  anybody
> ever tried to use it" situation means that the code should likely be
> excised.

The bug doesn't trigger on every read of /proc/slab_allocators (as noted
later in this thread by Qian).  I tried to repro it with a bunch of
different configs and often `cat /proc/slab_allocators` just returns
empty.

I've got a patchset ready to go sitting in my tree that removes SLAB, I
could just send it to start the conversation :)


	Tobin