From: Jann Horn jannh@google.com
[ Upstream commit bcc6244e13b4d4903511a1ea84368abf925031c0 ]
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@g... Signed-off-by: Sasha Levin sashal@kernel.org --- 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 ed92b75f7e024..fcdf8aaaa37cb 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -939,9 +939,10 @@ 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