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

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.

Note that the leak is not in the real world, and therefore no user is
impacted.  It is only potential for imaginaray damon_call() use cases that
do 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.

Link: https://lkml.kernel.org/r/20251202082340.34178-1-lienze@kylinos.cn
Fixes: 43df7676e550 ("mm/damon/core: introduce repeat mode damon_call()")
Signed-off-by: Enze Li <lienze@kylinos.cn>
Reviewed-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 84f80a20f2336edfc1161a7c517cc321f07cf9b1..c852cac4f82e9f27b2d78ba4da5da909e97bb6fc 100644 (file)
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -2606,13 +2606,19 @@ 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 */