There are a few places that call blocking primitives from wait loops,
provide infrastructure to support this without the typical
task_struct::state collision.
We record the wakeup in wait_queue_t::flags which leaves
task_struct::state free to be used by others.
Signed-off-by: Peter Zijlstra <pet...@infradead.org>
---
include/linux/wait.h | 7 ++++++-
kernel/sched/wait.c | 29 +++++++++++++++++++++++++++++
2 files changed, 35 insertions(+), 1 deletion(-)
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -13,9 +13,12 @@ typedef struct __wait_queue wait_queue_t
typedef int (*wait_queue_func_t)(wait_queue_t *wait, unsigned mode, int flags,
void *key);
int default_wake_function(wait_queue_t *wait, unsigned mode, int flags, void
*key);
+/* __wait_queue::flags */
+#define WQ_FLAG_EXCLUSIVE 0x01
+#define WQ_FLAG_WOKEN 0x02
+
struct __wait_queue {
unsigned int flags;
-#define WQ_FLAG_EXCLUSIVE 0x01
void *private;
wait_queue_func_t func;
struct list_head task_list;
@@ -825,6 +828,8 @@ void prepare_to_wait_exclusive(wait_queu
long prepare_to_wait_event(wait_queue_head_t *q, wait_queue_t *wait, int
state);
void finish_wait(wait_queue_head_t *q, wait_queue_t *wait);
void abort_exclusive_wait(wait_queue_head_t *q, wait_queue_t *wait, unsigned
int mode, void *key);
+long wait_woken(wait_queue_t *wait, unsigned mode, long timeout);
+int woken_wake_function(wait_queue_t *wait, unsigned mode, int sync, void
*key);
int autoremove_wake_function(wait_queue_t *wait, unsigned mode, int sync, void
*key);
int wake_bit_function(wait_queue_t *wait, unsigned mode, int sync, void *key);
--- a/kernel/sched/wait.c
+++ b/kernel/sched/wait.c
@@ -297,6 +297,35 @@ int autoremove_wake_function(wait_queue_
}
EXPORT_SYMBOL(autoremove_wake_function);
+long wait_woken(wait_queue_t *wait, unsigned mode, long timeout)
+{
+ set_current_state(mode);
+ if (!(wait->flags & WQ_FLAG_WOKEN))
+ timeout = schedule_timeout(timeout);
+ else
+ wait->flags &= ~WQ_FLAG_WOKEN;
+ __set_current_state(TASK_RUNNING);
+
+ return timeout;
+}
+EXPORT_SYMBOL(wait_woken);
+
+int woken_wake_function(wait_queue_t *wait, unsigned mode, int sync, void *key)
+{
+ /*
+ * Although this function is called under waitqueue lock, LOCK
+ * doesn't imply write barrier and the users expect write
+ * barrier semantics on wakeup functions. The following
+ * smp_wmb() is equivalent to smp_wmb() in try_to_wake_up()
+ * and is paired with set_mb() in wait_woken().
+ */
+ smp_wmb();
+ wait->flags |= WQ_FLAG_WOKEN;
+
+ return default_wake_function(wait, mode, sync, key);
+}
+EXPORT_SYMBOL(woken_wake_function);
+
int wake_bit_function(wait_queue_t *wait, unsigned mode, int sync, void *arg)
{
struct wait_bit_key *key = arg;
--
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