Commit bcc6244e authored by Jann Horn's avatar Jann Horn Committed by Peter Zijlstra
Browse files

sched: Clarify wake_up_q()'s write to task->wake_q.next 



Clarify that wake_up_q() does an atomic write to task->wake_q.next, after
which a concurrent __wake_q_add() can immediately overwrite
task->wake_q.next again.

Signed-off-by: default avatarJann Horn <jannh@google.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20250129-sched-wakeup-prettier-v1-1-2f51f5f663fa@google.com
parent 9065ce69

kernel/sched/core.c

+3 −2
Original line number Diff line number Diff line
@@ -1055,9 +1055,10 @@ void wake_up_q(struct wake_q_head *head) 
		struct task_struct *task;



		task = container_of(node, struct task_struct, wake_q);

		/* Task can safely be re-inserted now: */

		node = node->next;

		task->wake_q.next = NULL;

		/* pairs with cmpxchg_relaxed() in __wake_q_add() */

		WRITE_ONCE(task->wake_q.next, NULL);

		/* Task can safely be re-inserted now. */



		/*

		 * wake_up_process() executes a full barrier, which pairs with