[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20181109102536.GE5321@dhcp22.suse.cz>
Date: Fri, 9 Nov 2018 11:25:36 +0100
From: Michal Hocko <mhocko@...nel.org>
To: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc: Kyungtae Kim <kt0755@...il.com>, akpm@...ux-foundation.org,
pavel.tatashin@...rosoft.com, vbabka@...e.cz, osalvador@...e.de,
rppt@...ux.vnet.ibm.com, aaron.lu@...el.com,
iamjoonsoo.kim@....com, alexander.h.duyck@...ux.intel.com,
mgorman@...hsingularity.net, lifeasageek@...il.com,
threeearcat@...il.com, syzkaller@...glegroups.com,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Subject: Re: UBSAN: Undefined behaviour in mm/page_alloc.c
On Fri 09-11-18 19:07:49, Tetsuo Handa wrote:
> On 2018/11/09 18:56, Michal Hocko wrote:
> > Does this following look better?
>
> Yes.
>
> >> Also, why not to add BUG_ON(gfp_mask & __GFP_NOFAIL); here?
> >
> > Because we do not want to blow up the kernel just because of a stupid
> > usage of the allocator. Can you think of an example where it would
> > actually make any sense?
> >
> > I would argue that such a theoretical abuse would blow up on an
> > unchecked NULL ptr access. Isn't that enough?
>
> We after all can't avoid blowing up the kernel even if we don't add BUG_ON().
> Stopping with BUG_ON() is saner than NULL pointer dereference messages.
I disagree (strongly to be more explicit). You never know the context
the allocator is called from. We do not want to oops with a random state
(locks heled etc). If the access blows up in the user then be it, the
bug will be clear and to be fixed but BUG_ON on an invalid core kernel
function is just a bad idea. I believe Linus was quite explicit about it
and I fully agree with him.
Besides that this is really off-topic to the issue at hands. Don't you
think?
--
Michal Hocko
SUSE Labs
Powered by blists - more mailing lists