linux-kernel - Re: [PATCH] slab: fix a crash by reading /proc/slab

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Message-ID: <01000169fd847a25-5933cc1e-a520-416a-b634-84b3e7ce9960-000000@email.amazonses.com>
Date:   Mon, 8 Apr 2019 15:15:11 +0000
From:   Christopher Lameter <cl@...ux.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
cc:     Qian Cai <cai@....pw>, Andrew Morton <akpm@...ux-foundation.org>,
        penberg@...nel.org, David Rientjes <rientjes@...gle.com>,
        iamjoonsoo.kim@....com, Tejun Heo <tj@...nel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] slab: fix a crash by reading /proc/slab_allocators

On Sun, 7 Apr 2019, Linus Torvalds wrote:

> On Sat, Apr 6, 2019 at 12:59 PM Qian Cai <cai@....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.

This is only occurring with specially build kernels so that memory leaks
can be investigated. The same is done with other tools (kasan and friends)
today I guess and also the SLUB debugging tools are much more user
friendly. So this means that some esoteric debugging feature of SLAB was
broken.