From: Vlastimil Babka <vbabka@suse.cz>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: Yangtao Li <tiny.windzz@gmail.com>,
Christoph Lameter <cl@linux.com>,
Pekka Enberg <penberg@kernel.org>,
David Rientjes <rientjes@google.com>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Andrew Morton <akpm@linux-foundation.org>,
Linux-MM <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm, slab: remove unnecessary unlikely()
Date: Tue, 6 Nov 2018 09:54:49 +0100 [thread overview]
Message-ID: <a16bb44b-5231-97fe-920d-20cd92b5f3b2@suse.cz> (raw)
In-Reply-To: <CACT4Y+a+7gqs+gdfePuVGZ-bDGvb8ieE8ugA-pK1AZ8HwfecQg@mail.gmail.com>
On 11/6/18 6:38 AM, Dmitry Vyukov wrote:
> On Mon, Nov 5, 2018 at 11:18 AM, Vlastimil Babka <vbabka@suse.cz> wrote:
>> +CC Dmitry
>>
>> On 11/4/18 1:50 PM, Yangtao Li wrote:
>>> WARN_ON() already contains an unlikely(), so it's not necessary to use
>>> unlikely.
>>>
>>> Signed-off-by: Yangtao Li <tiny.windzz@gmail.com>
>>
>> Acked-by: Vlastimil Babka <vbabka@suse.cz>
>>
>> Maybe also change it back to WARN_ON_ONCE? I already considered it while
>> reviewing Dmitry's patch and wasn't sure. Now I think that what can
>> happen is that either a kernel bug is introduced that _ONCE is enough to
>> catch (two separate bugs introduced to both hit this would be rare, and
>> in that case the second one will be reported after the first one is
>> fixed), or this gets called with a user-supplied value, and then we want
>> to avoid spamming dmesg with multiple warnings that the user could
>> trigger at will.
>
>
> If you asking me, I am fine both changes.
> I was mainly interested in removing the bogus warnings that actually fire.
OK thanks. Andrew can you update the patch to WARN_ON_ONCE?
Changelog addition:
Also change WARN_ON() back to WARN_ON_ONCE() to avoid potentially
spamming dmesg with user-triggerable large allocations.
>
>>> ---
>>> mm/slab_common.c | 4 +---
>>> 1 file changed, 1 insertion(+), 3 deletions(-)
>>>
>>> diff --git a/mm/slab_common.c b/mm/slab_common.c
>>> index 7eb8dc136c1c..4f54684f5435 100644
>>> --- a/mm/slab_common.c
>>> +++ b/mm/slab_common.c
>>> @@ -1029,10 +1029,8 @@ struct kmem_cache *kmalloc_slab(size_t size, gfp_t flags)
>>>
>>> index = size_index[size_index_elem(size)];
>>> } else {
>>> - if (unlikely(size > KMALLOC_MAX_CACHE_SIZE)) {
>>> - WARN_ON(1);
>>> + if (WARN_ON(size > KMALLOC_MAX_CACHE_SIZE))
>>> return NULL;
>>> - }
>>> index = fls(size - 1);
>>> }
>>>
>>>
>>
next prev parent reply other threads:[~2018-11-06 8:54 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-04 12:50 [PATCH] mm, slab: remove unnecessary unlikely() Yangtao Li
2018-11-05 10:18 ` Vlastimil Babka
2018-11-06 5:38 ` Dmitry Vyukov
2018-11-06 8:54 ` Vlastimil Babka [this message]
2018-11-07 22:55 ` David Rientjes
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