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From: Michal Hocko <mhocko@kernel.org>
To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Vlastimil Babka <vbabka@suse.cz>, Kyungtae Kim <kt0755@gmail.com>,
	akpm@linux-foundation.org, pavel.tatashin@microsoft.com,
	osalvador@suse.de, rppt@linux.vnet.ibm.com, aaron.lu@intel.com,
	iamjoonsoo.kim@lge.com, alexander.h.duyck@linux.intel.com,
	mgorman@techsingularity.net, lifeasageek@gmail.com,
	threeearcat@gmail.com, syzkaller@googlegroups.com,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Subject: Re: UBSAN: Undefined behaviour in mm/page_alloc.c
Date: Fri, 9 Nov 2018 11:28:55 +0100
Message-ID: <20181109102855.GF5321@dhcp22.suse.cz> (raw)
In-Reply-To: <9e17d033-b2ab-3edb-ae0b-90d4f713e55b@i-love.sakura.ne.jp>

On Fri 09-11-18 19:24:48, Tetsuo Handa wrote:
> On 2018/11/09 19:10, Vlastimil Babka wrote:>>>> +	 * reclaim >= MAX_ORDER areas which will never succeed. Callers may
> >>>> +	 * be using allocators in order of preference for an area that is
> >>>> +	 * too large.
> >>>> +	 */
> >>>> +	if (order >= MAX_ORDER) {
> >>>
> >>> 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?
> > 
> > Agreed.
> > 
> 
> If someone has written a module with __GFP_NOFAIL for an architecture
> where PAGE_SIZE == 2048KB, and someone else tried to use that module on
> another architecture where PAGE_SIZE == 4KB. You are saying that
> triggering NULL pointer dereference is a fault of that user's ignorance
> about MM. You are saying that everyone knows internal of MM. Sad...

What kind of argument is this? Seriously! We do consider GFP_NOFAIL
problematic even for !order-0 requests and warn appropriately. Talking
about anything getting close to MAX_ORDER is just a crazy talk. In any
case this is largely tangential to the issue reported here.
-- 
Michal Hocko
SUSE Labs

  reply index

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-09  4:09 Kyungtae Kim
2018-11-09  8:42 ` Vlastimil Babka
2018-11-09  8:43 ` Michal Hocko
2018-11-09  9:41   ` Tetsuo Handa
2018-11-09  9:56     ` Michal Hocko
2018-11-09 10:07       ` Tetsuo Handa
2018-11-09 10:25         ` Michal Hocko
2018-11-09 10:10       ` Vlastimil Babka
2018-11-09 10:22         ` Michal Hocko
2018-11-09 10:24         ` Tetsuo Handa
2018-11-09 10:28           ` Michal Hocko [this message]
2018-11-09 10:52       ` Balbir Singh
2018-11-09  9:56   ` Mel Gorman
2018-11-13  9:43   ` Michal Hocko
2018-11-13 23:15     ` Andrew Morton
2018-11-13 23:23       ` Vlastimil Babka
2018-11-13 23:32         ` Andrew Morton
2018-11-14  0:05           ` Vlastimil Babka
2018-11-19 23:57             ` Pavel Machek
2018-11-13 23:29     ` Andrew Morton
2018-11-14  7:10       ` Michal Hocko
2018-11-16 23:43       ` Dmitry Vyukov

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