The following commit has been merged into the sched/urgent branch of tip: Commit-ID: bcc6244e13b4d4903511a1ea84368abf925031c0 Gitweb: https://git.kernel.org/tip/bcc6244e13b4d4903511a1ea84368abf925031c0 Author: Jann Horn <jannh@xxxxxxxxxx> AuthorDate: Wed, 29 Jan 2025 20:53:03 +01:00 Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx> CommitterDate: Sat, 08 Feb 2025 15:43:12 +01:00 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: Jann Horn <jannh@xxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Link: https://lkml.kernel.org/r/20250129-sched-wakeup-prettier-v1-1-2f51f5f663fa@xxxxxxxxxx --- kernel/sched/core.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 3e5a6bf..8931d9b 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -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
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