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-rw-r--r--include/linux/wait.h26
1 files changed, 26 insertions, 0 deletions
diff --git a/include/linux/wait.h b/include/linux/wait.h
index 2d0df57c9902..851e07da2583 100644
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -217,6 +217,7 @@ void __wake_up_sync_key(struct wait_queue_head *wq_head, unsigned int mode, void
void __wake_up_locked_sync_key(struct wait_queue_head *wq_head, unsigned int mode, void *key);
void __wake_up_locked(struct wait_queue_head *wq_head, unsigned int mode, int nr);
void __wake_up_sync(struct wait_queue_head *wq_head, unsigned int mode);
+void __wake_up_pollfree(struct wait_queue_head *wq_head);
#define wake_up(x) __wake_up(x, TASK_NORMAL, 1, NULL)
#define wake_up_nr(x, nr) __wake_up(x, TASK_NORMAL, nr, NULL)
@@ -245,6 +246,31 @@ void __wake_up_sync(struct wait_queue_head *wq_head, unsigned int mode);
#define wake_up_interruptible_sync_poll_locked(x, m) \
__wake_up_locked_sync_key((x), TASK_INTERRUPTIBLE, poll_to_key(m))
+/**
+ * wake_up_pollfree - signal that a polled waitqueue is going away
+ * @wq_head: the wait queue head
+ *
+ * In the very rare cases where a ->poll() implementation uses a waitqueue whose
+ * lifetime is tied to a task rather than to the 'struct file' being polled,
+ * this function must be called before the waitqueue is freed so that
+ * non-blocking polls (e.g. epoll) are notified that the queue is going away.
+ *
+ * The caller must also RCU-delay the freeing of the wait_queue_head, e.g. via
+ * an explicit synchronize_rcu() or call_rcu(), or via SLAB_TYPESAFE_BY_RCU.
+ */
+static inline void wake_up_pollfree(struct wait_queue_head *wq_head)
+{
+ /*
+ * For performance reasons, we don't always take the queue lock here.
+ * Therefore, we might race with someone removing the last entry from
+ * the queue, and proceed while they still hold the queue lock.
+ * However, rcu_read_lock() is required to be held in such cases, so we
+ * can safely proceed with an RCU-delayed free.
+ */
+ if (waitqueue_active(wq_head))
+ __wake_up_pollfree(wq_head);
+}
+
#define ___wait_cond_timeout(condition) \
({ \
bool __cond = (condition); \