The patch titled Subject: mm/damon/core: fix list_add_tail() call on damon_call() has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-damon-core-fix-list_add_tail-call-on-damon_call.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: SeongJae Park sj@kernel.org Subject: mm/damon/core: fix list_add_tail() call on damon_call() Date: Tue, 14 Oct 2025 13:59:36 -0700

Each damon_ctx maintains callback requests using a linked list (damon_ctx->call_controls). When a new callback request is received via damon_call(), the new request should be added to the list. However, the function is making a mistake at list_add_tail() invocation: putting the new item to add and the list head to add it before, in the opposite order. Because of the linked list manipulation implementation, the new request can still be reached from the context's list head. But the list items that were added before the new request are dropped from the list.

As a result, the callbacks are unexpectedly not invocated. Worse yet, if the dropped callback requests were dynamically allocated, the memory is leaked. Actually DAMON sysfs interface is using a dynamically allocated repeat-mode callback request for automatic essential stats update. And because the online DAMON parameters commit is using a non-repeat-mode callback request, the issue can easily be reproduced, like below.

# damo start --damos_action stat --refresh_stat 1s # damo tune --damos_action stat --refresh_stat 1s

The first command dynamically allocates the repeat-mode callback request for automatic essential stat update. Users can see the essential stats are automatically updated for every second, using the sysfs interface.

The second command calls damon_commit() with a new callback request that was made for the commit. As a result, the previously added repeat-mode callback request is dropped from the list. The automatic stats refresh stops working, and the memory for the repeat-mode callback request is leaked. It can be confirmed using kmemleak.

Fix the mistake on the list_add_tail() call.

Link: https://lkml.kernel.org/r/20251014205939.1206-1-sj@kernel.org Fixes: 004ded6bee11 ("mm/damon: accept parallel damon_call() requests") Signed-off-by: SeongJae Park sj@kernel.org Cc: stable@vger.kernel.org [6.17+] Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/damon/core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/damon/core.c~mm-damon-core-fix-list_add_tail-call-on-damon_call +++ a/mm/damon/core.c @@ -1450,7 +1450,7 @@ int damon_call(struct damon_ctx *ctx, st INIT_LIST_HEAD(&control->list);

mutex_lock(&ctx->call_controls_lock); - list_add_tail(&ctx->call_controls, &control->list); + list_add_tail(&control->list, &ctx->call_controls); mutex_unlock(&ctx->call_controls_lock); if (!damon_is_running(ctx)) return -EINVAL; _

Patches currently in -mm which might be from sj@kernel.org are

mm-damon-sysfs-catch-commit-test-ctx-alloc-failure.patch mm-damon-sysfs-dealloc-commit-test-ctx-always.patch mm-damon-core-fix-list_add_tail-call-on-damon_call.patch mm-zswap-remove-unnecessary-dlen-writes-for-incompressible-pages.patch mm-zswap-fix-typos-s-zwap-zswap.patch mm-zswap-s-red-black-tree-xarray.patch docs-admin-guide-mm-zswap-s-red-black-tree-xarray.patch