linux-kernel - Re: [PATCH 1/3] slab: check the return value of check_bytes_and

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Message-ID: <0df9277d-6f10-4af6-abd7-50a275489a72@linux.dev>
Date: Mon, 3 Jun 2024 16:05:41 +0800
From: Chengming Zhou <chengming.zhou@...ux.dev>
To: Vlastimil Babka <vbabka@...e.cz>,
 "Christoph Lameter (Ampere)" <cl@...two.org>
Cc: Pekka Enberg <penberg@...nel.org>, David Rientjes <rientjes@...gle.com>,
 Joonsoo Kim <iamjoonsoo.kim@....com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Roman Gushchin <roman.gushchin@...ux.dev>,
 Hyeonggon Yoo <42.hyeyoo@...il.com>, Feng Tang <feng.tang@...el.com>,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org, zhouchengming@...edance.com
Subject: Re: [PATCH 1/3] slab: check the return value of
 check_bytes_and_report()

On 2024/6/3 15:46, Vlastimil Babka wrote:
> On 5/31/24 10:31 AM, Chengming Zhou wrote:
>> On 2024/5/30 23:20, Christoph Lameter (Ampere) wrote:
>>> On Tue, 28 May 2024, Chengming Zhou wrote:
>>>
>>>> diff --git a/mm/slub.c b/mm/slub.c
>>>> index 0809760cf789..de57512734ac 100644
>>>> --- a/mm/slub.c
>>>> +++ b/mm/slub.c
>>>> @@ -1324,9 +1324,10 @@ static int check_object(struct kmem_cache *s, struct slab *slab,
>>>>         }
>>>>     } else {
>>>>         if ((s->flags & SLAB_POISON) && s->object_size < s->inuse) {
>>>> -            check_bytes_and_report(s, slab, p, "Alignment padding",
>>>> +            if (!check_bytes_and_report(s, slab, p, "Alignment padding",
>>>>                 endobject, POISON_INUSE,
>>>> -                s->inuse - s->object_size);
>>>> +                s->inuse - s->object_size))
>>>> +                return 0;
>>>>         }
>>>>     }
>>>
>>> This change means we will then skip the rest of the checks in check_object() such as the poison check.
>>
>> Yeah, only when this padding checking failed.
>>
>> Now, we always abort checking and return 0 when the first checking error happens,
>> such as redzones checking above.
> 
> Yes your patch will make it consistent. But IMHO it would be better to do
> all the checks without skipping, report their specific error findings in
> check_bytes_and_report() but not print_trailer(). Once all checks were done,
> if any found an error, print the trailer once from check_object(). Thoughts?

Ok, it's feasible, will change to this.

> 
>> Thanks.
>