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From: Oscar Salvador <osalvador@suse.de>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org,
	linux-mm@kvack.org,
	Michal Hocko <mhocko@suse.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	Marco Elver <elver@google.com>,
	Andrey Konovalov <andreyknvl@gmail.com>,
	Alexander Potapenko <glider@google.com>,
	Alexandre Ghiti <alexghiti@rivosinc.com>,
	Oscar Salvador <osalvador@suse.de>
Subject: [PATCH v4 4/4] mm,page_owner: Fix printing of stack records
Date: Thu,  4 Apr 2024 09:07:02 +0200
Message-ID: <20240404070702.2744-5-osalvador@suse.de>
In-Reply-To: <20240404070702.2744-1-osalvador@suse.de>
References: <20240404070702.2744-1-osalvador@suse.de>
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When seq_* code sees that its buffer overflowed, it re-allocates a bigger
onecand calls seq_operations->start() callback again.
stack_start() naively though that if it got called again, it meant that the
old record got already printed so it returned the next object, but that is
not true.

The consequence of that is that every time stack_stop() -> stack_start()
get called because we needed a bigger buffer, stack_start() will skip
entries, and those will not be printed.

Fix it by not advancing to the next object in stack_start().

Fixes: 765973a09803 ("mm,page_owner: display all stacks and their count")
Signed-off-by: Oscar Salvador <osalvador@suse.de>
---
 mm/page_owner.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/mm/page_owner.c b/mm/page_owner.c
index b4476f45b376..9bef0b442863 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -872,13 +872,11 @@ static void *stack_start(struct seq_file *m, loff_t *ppos)
 		 * value of stack_list.
 		 */
 		stack = smp_load_acquire(&stack_list);
+		m->private = stack;
 	} else {
 		stack = m->private;
-		stack = stack->next;
 	}
 
-	m->private = stack;
-
 	return stack;
 }
 
-- 
2.44.0