linux-kernel - [PATCH mm,percpu_ref,rcu 2/6] mm: Make mem_dump_obj() handle NULL and zero-sized pointers

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Date:   Tue,  5 Jan 2021 17:17:46 -0800
From:   paulmck@...nel.org
To:     linux-kernel@...r.kernel.org, rcu@...r.kernel.org,
        linux-mm@...ck.org
Cc:     cl@...ux.com, penberg@...nel.org, rientjes@...gle.com,
        iamjoonsoo.kim@....com, akpm@...ux-foundation.org,
        ming.lei@...hat.com, axboe@...nel.dk, kernel-team@...com,
        "Paul E. McKenney" <paulmck@...nel.org>
Subject: [PATCH mm,percpu_ref,rcu 2/6] mm: Make mem_dump_obj() handle NULL and zero-sized pointers

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>
Acked-by: Vlastimil Babka <vbabka@...e.cz>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 mm/util.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/mm/util.c b/mm/util.c
index da46f9d..92f23d2 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -997,7 +997,12 @@ 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)) {
-- 
2.9.5