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().
Fixes: 0f91d13366a4 ("mm/damon: simplify stop mechanism") Reported-by: Jakub Acs acsjakub@amazon.de Cc: stable@vger.kernel.org # 5.15.x Signed-off-by: SeongJae Park sj@kernel.org --- Note that the report has not publicly made, so this patch doesn't have a Closes: tag.
include/linux/damon.h | 2 ++ mm/damon/core.c | 6 ++++++ 2 files changed, 8 insertions(+)
diff --git a/include/linux/damon.h b/include/linux/damon.h index aa34ab433bc5..12510d8c51c6 100644 --- a/include/linux/damon.h +++ b/include/linux/damon.h @@ -579,6 +579,8 @@ 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; diff --git a/mm/damon/core.c b/mm/damon/core.c index f91715a58dc7..2c0cc65d041e 100644 --- a/mm/damon/core.c +++ b/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_ctx *ctx) 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); @@ -1483,6 +1488,7 @@ 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)