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@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # 5.15.x
Signed-off-by: SeongJae Park <sj@xxxxxxxxxx>
---
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)
--
2.34.1
