Commit 6376a824 authored by SeongJae Park's avatar SeongJae Park Committed by Andrew Morton
Browse files

mm/damon/core: make damon_start() waits until kdamond_fn() starts 

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
0f91d133 ("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: 0f91d133 ("mm/damon: simplify stop mechanism")
Signed-off-by: default avatarSeongJae Park <sj@kernel.org>
Reported-by: default avatarJakub 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: default avatarAndrew Morton <akpm@linux-foundation.org>
parent a6fcd57c

include/linux/damon.h

+2 −0
Original line number Diff line number Diff line
@@ -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;

mm/damon/core.c

+6 −0
Original line number Diff line number Diff line
@@ -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);
@@ -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)