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

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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: Jann Horn <jannh@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20250129-sched-wakeup-prettier-v1-1-2f51f5f663fa@google.com
This commit is contained in:
Jann Horn 2025-01-29 20:53:03 +01:00 • committed by Peter Zijlstra
parent 9065ce6975
commit bcc6244e13
1 changed files with 3 additions and 2 deletions
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5
kernel/sched/core.c
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@ -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