Merge tag 'v5.8.5' into dev-5.8dev-5.8

This is the 5.8.5 stable release

Signed-off-by: Joel Stanley <joel@jms.id.au>

1 files changed, 15 insertions, 1 deletions

diff --git a/kernel/signal.c b/kernel/signal.c
index 6f16f7c5d375..42b67d2cea37 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -2541,7 +2541,21 @@ bool get_signal(struct ksignal *ksig)
 
 relock:
 	spin_lock_irq(&sighand->siglock);
-	current->jobctl &= ~JOBCTL_TASK_WORK;
+	/*
+	 * Make sure we can safely read ->jobctl() in task_work add. As Oleg
+	 * states:
+	 *
+	 * It pairs with mb (implied by cmpxchg) before READ_ONCE. So we
+	 * roughly have
+	 *
+	 *	task_work_add:				get_signal:
+	 *	STORE(task->task_works, new_work);	STORE(task->jobctl);
+	 *	mb();					mb();
+	 *	LOAD(task->jobctl);			LOAD(task->task_works);
+	 *
+	 * and we can rely on STORE-MB-LOAD [ in task_work_add].
+	 */
+	smp_store_mb(current->jobctl, current->jobctl & ~JOBCTL_TASK_WORK);
 	if (unlikely(current->task_works)) {
 		spin_unlock_irq(&sighand->siglock);
 		task_work_run();