The quilt patch titled Subject: mm/damon/core: make damon_start() waits until kdamond_fn() starts has been removed from the -mm tree. Its filename was mm-damon-core-make-damon_start-waits-until-kdamond_fn-starts.patch

This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------ From: SeongJae Park sj@kernel.org Subject: mm/damon/core: make damon_start() waits until kdamond_fn() starts Date: Fri, 8 Dec 2023 17:50:18 +0000

The cleanup tasks of kdamond threads including reset of corresponding DAMON context's ->kdamond field and decrease of global nr_running_ctxs counter is supposed to be executed by kdamond_fn(). However, commit 0f91d13366a4 ("mm/damon: simplify stop mechanism") made neither damon_start() nor damon_stop() ensure the corresponding kdamond has started the execution of kdamond_fn().

As a result, the cleanup can be skipped if damon_stop() is called fast enough after the previous damon_start(). Especially the skipped reset of ->kdamond could cause a use-after-free.

Fix it by waiting for start of kdamond_fn() execution from damon_start().

Link: https://lkml.kernel.org/r/20231208175018.63880-1-sj@kernel.org Fixes: 0f91d13366a4 ("mm/damon: simplify stop mechanism") Signed-off-by: SeongJae Park sj@kernel.org Reported-by: Jakub Acs acsjakub@amazon.de Cc: Changbin Du changbin.du@intel.com Cc: Jakub Acs acsjakub@amazon.de Cc: stable@vger.kernel.org # 5.15.x Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

include/linux/damon.h | 2 ++ mm/damon/core.c | 6 ++++++ 2 files changed, 8 insertions(+)

--- a/include/linux/damon.h~mm-damon-core-make-damon_start-waits-until-kdamond_fn-starts +++ a/include/linux/damon.h @@ -559,6 +559,8 @@ struct damon_ctx { * update */ unsigned long next_ops_update_sis; + /* for waiting until the execution of the kdamond_fn is started */ + struct completion kdamond_started;

/* public: */ struct task_struct *kdamond; --- a/mm/damon/core.c~mm-damon-core-make-damon_start-waits-until-kdamond_fn-starts +++ a/mm/damon/core.c @@ -445,6 +445,8 @@ struct damon_ctx *damon_new_ctx(void) if (!ctx) return NULL;

+ init_completion(&ctx->kdamond_started); + ctx->attrs.sample_interval = 5 * 1000; ctx->attrs.aggr_interval = 100 * 1000; ctx->attrs.ops_update_interval = 60 * 1000 * 1000; @@ -668,11 +670,14 @@ static int __damon_start(struct damon_ct mutex_lock(&ctx->kdamond_lock); if (!ctx->kdamond) { err = 0; + reinit_completion(&ctx->kdamond_started); ctx->kdamond = kthread_run(kdamond_fn, ctx, "kdamond.%d", nr_running_ctxs); if (IS_ERR(ctx->kdamond)) { err = PTR_ERR(ctx->kdamond); ctx->kdamond = NULL; + } else { + wait_for_completion(&ctx->kdamond_started); } } mutex_unlock(&ctx->kdamond_lock); @@ -1433,6 +1438,7 @@ static int kdamond_fn(void *data)

pr_debug("kdamond (%d) starts\n", current->pid);

+ complete(&ctx->kdamond_started); kdamond_init_intervals_sis(ctx);

if (ctx->ops.init) _

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

selftests-damon-implement-a-python-module-for-test-purpose-damon-sysfs-controls.patch selftests-damon-_damon_sysfs-implement-kdamonds-start-function.patch selftests-damon-_damon_sysfs-implement-updat_schemes_tried_bytes-command.patch selftests-damon-add-a-test-for-update_schemes_tried_regions-sysfs-command.patch selftests-damon-add-a-test-for-update_schemes_tried_regions-hang-bug.patch