linux-kernel - Re: [PATCH v3 1/2] mm: Provide empty function for kmem_dump_obj() when CONFIG

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Message-ID: <91233a90-94bb-0318-3bcb-10a4403cd526@huaweicloud.com>
Date:   Wed, 2 Aug 2023 19:11:04 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...weicloud.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>, linux-mm@...ck.org,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Josh Triplett <josh@...htriplett.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Zqiang <qiang.zhang1211@...il.com>, rcu@...r.kernel.org,
        linux-kernel@...r.kernel.org, openeuler <kernel@...neuler.org>
Subject: Re: [PATCH v3 1/2] mm: Provide empty function for kmem_dump_obj()
 when CONFIG_PRINTK=n



On 2023/8/2 11:57, Matthew Wilcox wrote:
> On Wed, Aug 02, 2023 at 11:45:16AM +0800, thunder.leizhen@...weicloud.com wrote:
>> +++ b/include/linux/slab.h
>> @@ -246,6 +246,9 @@ size_t ksize(const void *objp);
>>  #ifdef CONFIG_PRINTK
>>  bool kmem_valid_obj(void *object);
>>  void kmem_dump_obj(void *object);
>> +#else
>> +static inline bool kmem_valid_obj(void *object) { return false; }
> 
> That is very confusing.  kmem_valid_obj() looks like a function which
> should exist regardless of CONFIG_PRINTK and to have it always return
> false if CONFIG_PRINTK isn't set seems weird.

Yes, I noticed it, but I didn't come up with a good idea.

> 
> I see we have one caller of kmem_valid_obj() right now.  Which means it
> shouldn't be an EXPORT_SYMBOL since that caller is not a module.
> 
> I think the right solution is to convert kmem_dump_obj() to
> work the same way as vmalloc_dump_obj().  ie:

Okay, it's a good suggestion.

In fact, kmem_dump_obj() also does what kmem_valid_obj() does, except
that it will print warning if the check fails. So, do as you suggest,
the duplicated code can be eliminated.

> 
> +++ b/mm/util.c
> @@ -1057,11 +1057,8 @@ void mem_dump_obj(void *object)
>  {
>         const char *type;
> 
> -       if (kmem_valid_obj(object)) {
> -               kmem_dump_obj(object);
> +       if (kmem_dump_obj(object))
>                 return;
> -       }
> -
>         if (vmalloc_dump_obj(object))
>                 return;
> 
> ... with corresponding changes to eliminate kmem_valid_obj() as a
> symbol.
> 
> .
> 

-- 
Regards,
  Zhen Lei