Commit 29492829 authored Jun 04, 2022 by SeongJae Park Committed by Andrew Morton Jun 16, 2022

mm/damon/reclaim: schedule 'damon_reclaim_timer' only after 'system_wq' is initialized

Commit 059342d1 ("mm/damon/reclaim: fix the timer always stays
active") made DAMON_RECLAIM's 'enabled' parameter store callback,
'enabled_store()', to schedule 'damon_reclaim_timer'.  The scheduling uses
'system_wq', which is initialized in 'workqueue_init_early()'.  As kernel
parameters parsing function ('parse_args()') is called before
'workqueue_init_early()', 'enabled_store()' can be executed before
'workqueue_init_early()' and end up accessing the uninitialized
'system_wq'.  As a result, the booting hang[1].  This commit fixes the
issue by checking if the initialization is done before scheduling the
timer.

[1] https://lkml.kernel.org/20220604192222.1488-1-sj@kernel.org/

Link: https://lkml.kernel.org/r/20220604195051.1589-1-sj@kernel.org


Fixes: 059342d1 ("mm/damon/reclaim: fix the timer always stays active")
Signed-off-by: SeongJae Park <sj@kernel.org>
Reported-by: Greg White <gwhite@kupulau.com>
Cc: Hailong Tu <tuhailong@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

parent d25c83c6

mm/damon/reclaim.c

+8 −0

Original line number	Diff line number	Diff line
		@@ -374,6 +374,8 @@ static void damon_reclaim_timer_fn(struct work_struct *work)
		}
		static DECLARE_DELAYED_WORK(damon_reclaim_timer, damon_reclaim_timer_fn);

		static bool damon_reclaim_initialized;

		static int enabled_store(const char *val,
		const struct kernel_param *kp)
		{
		@@ -382,6 +384,10 @@ static int enabled_store(const char *val,
		if (rc < 0)
		return rc;

		/* system_wq might not initialized yet */
		if (!damon_reclaim_initialized)
		return rc;

		if (enabled)
		schedule_delayed_work(&damon_reclaim_timer, 0);

		@@ -449,6 +455,8 @@ static int __init damon_reclaim_init(void)
		damon_add_target(ctx, target);

		schedule_delayed_work(&damon_reclaim_timer, 0);

		damon_reclaim_initialized = true;
		return 0;
		}