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Subject: Re: [PATCH v3 1/2] mm: Provide empty function for kmem_dump_obj()
 when CONFIG_PRINTK=n
To:     Matthew Wilcox <willy@infradead.org>
Cc:     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>,
        Vlastimil Babka <vbabka@suse.cz>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Hyeonggon Yoo <42.hyeyoo@gmail.com>, linux-mm@kvack.org,
        "Paul E . McKenney" <paulmck@kernel.org>,
        Frederic Weisbecker <frederic@kernel.org>,
        Neeraj Upadhyay <quic_neeraju@quicinc.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Josh Triplett <josh@joshtriplett.org>,
        Boqun Feng <boqun.feng@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        Zqiang <qiang.zhang1211@gmail.com>, rcu@vger.kernel.org,
        linux-kernel@vger.kernel.org, openeuler <kernel@openeuler.org>
References: <20230802034518.1115-1-thunder.leizhen@huaweicloud.com>
 <20230802034518.1115-2-thunder.leizhen@huaweicloud.com>
 <ZMnUR61eFmO014EL@casper.infradead.org>
From:   "Leizhen (ThunderTown)" <thunder.leizhen@huaweicloud.com>
Message-ID: <91233a90-94bb-0318-3bcb-10a4403cd526@huaweicloud.com>
Date:   Wed, 2 Aug 2023 19:11:04 +0800
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On 2023/8/2 11:57, Matthew Wilcox wrote:
> On Wed, Aug 02, 2023 at 11:45:16AM +0800, thunder.leizhen@huaweicloud.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