[PATCH 7.2.y 2/3] mm/kmemleak: stop the task stack scan early when interrupted

[Sasha Levin <sashal@kernel.org>]

From: Breno Leitao <leitao@debian.org>

[ Upstream commit eb11f56eeca56069613d00bf623607e305b271d9 ]

scan_block() already checks scan_should_stop() for every pointer and bails
out of the current block, but the task stack walk cannot tell and keeps
issuing a separate scan_should_stop() between every task.

Return that status from scan_block() and use it as the task stack loop
condition, so the walk stops as soon as a scan is interrupted.

Link: https://lore.kernel.org/20260615-kmemleak-stack-resched-v3-2-acecd7d7fd92@debian.org
Signed-off-by: Breno Leitao <leitao@debian.org>
Suggested-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Qian Cai <cai@lca.pw>
Cc: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Stable-dep-of: 3541a2b06ecd ("mm/kmemleak: report RCU-tasks quiescent states during the scan")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 mm/kmemleak.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 16b72cead07d2..bc79e293531b7 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -1525,22 +1525,25 @@ static int scan_should_stop(void)
 
 /*
  * Scan a memory block (exclusive range) for valid pointers and add those
- * found to the gray list.
+ * found to the gray list. Return non-zero if the scan was interrupted.
  */
-static void scan_block(void *_start, void *_end,
-		       struct kmemleak_object *scanned)
+static int scan_block(void *_start, void *_end,
+		      struct kmemleak_object *scanned)
 {
 	unsigned long *ptr;
 	unsigned long *start = PTR_ALIGN(_start, BYTES_PER_POINTER);
 	unsigned long *end = _end - (BYTES_PER_POINTER - 1);
 	unsigned long flags;
+	int stop = 0;
 
 	raw_spin_lock_irqsave(&kmemleak_lock, flags);
 	for (ptr = start; ptr < end; ptr++) {
 		unsigned long pointer;
 
-		if (scan_should_stop())
+		if (scan_should_stop()) {
+			stop = 1;
 			break;
+		}
 
 		kasan_disable_current();
 		pointer = *(unsigned long *)kasan_reset_tag((void *)ptr);
@@ -1550,6 +1553,8 @@ static void scan_block(void *_start, void *_end,
 		pointer_update_refs(scanned, pointer, OBJECT_PERCPU);
 	}
 	raw_spin_unlock_irqrestore(&kmemleak_lock, flags);
+
+	return stop;
 }
 
 /*
@@ -1705,6 +1710,7 @@ static void kmemleak_scan_task_stacks(void)
 {
 	struct pid *pid;
 	int nr = 1;
+	int stop = 0;
 
 	do {
 		struct task_struct *p = NULL;
@@ -1723,13 +1729,13 @@ static void kmemleak_scan_task_stacks(void)
 			void *stack = try_get_task_stack(p);
 
 			if (stack) {
-				scan_block(stack, stack + THREAD_SIZE, NULL);
+				stop = scan_block(stack, stack + THREAD_SIZE, NULL);
 				put_task_stack(p);
 			}
 			put_task_struct(p);
 		}
 		cond_resched();
-	} while (pid && !scan_should_stop());
+	} while (pid && !stop);
 }
 
 /*
-- 
2.53.0