[PATCH] mm/damon/core: fix memory leak of repeat mode damon_call_control objects

[PATCH] mm/damon/core: fix memory leak of repeat mode damon_call_control objects

[Enze Li]

A memory leak exists in the handling of repeat mode damon_call_control
objects by kdamond_call().  While damon_call() correctly allows multiple
repeat mode objects (with ->repeat set to true) to be added to the
per-context list, kdamond_call() incorrectly processes them.

The function moves all repeat mode objects from the context's list to a
temporary list (repeat_controls).  However, it only moves the first
object back to the context's list for future calls, leaving the
remaining objects on the temporary list where they are abandoned and
leaked.

This patch fixes the leak by ensuring all repeat mode objects are
properly re-added to the context's list.

Fixes: 43df7676e550 ("mm/damon/core: introduce repeat mode damon_call()")
Signed-off-by: Enze Li <lienze@kylinos.cn>
Cc: <stable@vger.kernel.org> # 6.17.x
---
 mm/damon/core.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 109b050c795a..66b5bae44f22 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -2526,13 +2526,19 @@ static void kdamond_call(struct damon_ctx *ctx, bool cancel)
 			list_add(&control->list, &repeat_controls);
 		}
 	}
-	control = list_first_entry_or_null(&repeat_controls,
-			struct damon_call_control, list);
-	if (!control || cancel)
-		return;
-	mutex_lock(&ctx->call_controls_lock);
-	list_add_tail(&control->list, &ctx->call_controls);
-	mutex_unlock(&ctx->call_controls_lock);
+	while (true) {
+		control = list_first_entry_or_null(&repeat_controls,
+				struct damon_call_control, list);
+		if (!control)
+			break;
+		/* Unlink from the repeate_controls list. */
+		list_del(&control->list);
+		if (cancel)
+			continue;
+		mutex_lock(&ctx->call_controls_lock);
+		list_add(&control->list, &ctx->call_controls);
+		mutex_unlock(&ctx->call_controls_lock);
+	}
 }
 
 /* Returns negative error code if it's not activated but should return */

base-commit: 7d0a66e4bb9081d75c82ec4957c50034cb0ea449
-- 
2.52.0

Re: [PATCH] mm/damon/core: fix memory leak of repeat mode damon_call_control objects

[SeongJae Park]

On Tue,  2 Dec 2025 16:23:40 +0800 Enze Li <lienze@kylinos.cn> wrote:

> A memory leak exists in the handling of repeat mode damon_call_control
> objects by kdamond_call().  While damon_call() correctly allows multiple
> repeat mode objects (with ->repeat set to true) to be added to the
> per-context list, kdamond_call() incorrectly processes them.
> 
> The function moves all repeat mode objects from the context's list to a
> temporary list (repeat_controls).  However, it only moves the first
> object back to the context's list for future calls, leaving the
> remaining objects on the temporary list where they are abandoned and
> leaked.

Thank you for quickly updating the description and sending this, Enze.  I think
it is also worthy to add the real user impact description.

Andrew, could you please add the below user impact description to the commit
message when you add this to the mm tree?

'''
Note that the leak is not in the real world, and therefore no user is impacted.
It is only potential for imagineray damon_call() use cases that not exist in
the tree for now.  In more detail, the leak happens only when the multiple
repeat mode objects are assumed to be deallocated by kdamond_call()
(damon_call_control->dealloc_on_cancel is set).  There is no such damon_call()
use cases at the moment.
'''

> 
> This patch fixes the leak by ensuring all repeat mode objects are
> properly re-added to the context's list.
> 
> Fixes: 43df7676e550 ("mm/damon/core: introduce repeat mode damon_call()")
> Signed-off-by: Enze Li <lienze@kylinos.cn>
> Cc: <stable@vger.kernel.org> # 6.17.x

Reviewed-by: SeongJae Park <sj@kernel.org>


Thanks,
SJ

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