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

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Date:   Wed, 2 Aug 2023 04:57:59 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     thunder.leizhen@...weicloud.com
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 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.

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:

+++ 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.