linux-kernel - Re: [PATCH v2 sl-b 2/5] mm: Make mem_dump_obj() handle NULL and zero-sized pointers

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Date:   Wed, 9 Dec 2020 18:48:47 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     paulmck@...nel.org, rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com, mingo@...nel.org,
        jiangshanlai@...il.com, akpm@...ux-foundation.org,
        mathieu.desnoyers@...icios.com, josh@...htriplett.org,
        tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
        dhowells@...hat.com, edumazet@...gle.com, fweisbec@...il.com,
        oleg@...hat.com, joel@...lfernandes.org, iamjoonsoo.kim@....com,
        andrii@...nel.org, Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>, linux-mm@...ck.org
Subject: Re: [PATCH v2 sl-b 2/5] mm: Make mem_dump_obj() handle NULL and
 zero-sized pointers

On 12/9/20 2:13 AM, paulmck@...nel.org wrote:
> From: "Paul E. McKenney" <paulmck@...nel.org>
> 
> This commit makes mem_dump_obj() call out NULL and zero-sized pointers
> specially instead of classifying them as non-paged memory.
> 
> Cc: Christoph Lameter <cl@...ux.com>
> Cc: Pekka Enberg <penberg@...nel.org>
> Cc: David Rientjes <rientjes@...gle.com>
> Cc: Joonsoo Kim <iamjoonsoo.kim@....com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: <linux-mm@...ck.org>
> Reported-by: Andrii Nakryiko <andrii@...nel.org>
> Signed-off-by: Paul E. McKenney <paulmck@...nel.org>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

> ---
>  mm/util.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/util.c b/mm/util.c
> index d0e60d2..8c2449f 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -985,7 +985,12 @@ int __weak memcmp_pages(struct page *page1, struct page *page2)
>  void mem_dump_obj(void *object)
>  {
>  	if (!virt_addr_valid(object)) {
> -		pr_cont(" non-paged (local) memory.\n");
> +		if (object == NULL)
> +			pr_cont(" NULL pointer.\n");
> +		else if (object == ZERO_SIZE_PTR)
> +			pr_cont(" zero-size pointer.\n");
> +		else
> +			pr_cont(" non-paged (local) memory.\n");
>  		return;
>  	}
>  	if (kmem_valid_obj(object)) {
>