There is a race between kthread_stop() and the new wait_woken() that
can result in a lack of progress.
CPU 0 | CPU 1
|
rfcomm_run() | kthread_stop()
... |
if (!test_bit(KTHREAD_SHOULD_STOP)) |
| set_bit(KTHREAD_SHOULD_STOP)
| wake_up_process()
wait_woken() | wait_for_completion()
set_current_state(INTERRUPTIBLE) |
if (!WQ_FLAG_WOKEN) |
schedule_timeout() |
|
After which both tasks will wait.. forever.
Fix this by having wait_woken() check for kthread_should_stop() but
only for kthreads (obviously).
Cc: Peter Hurley <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
---
kernel/sched/wait.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
--- a/kernel/sched/wait.c
+++ b/kernel/sched/wait.c
@@ -9,6 +9,7 @@
#include <linux/mm.h>
#include <linux/wait.h>
#include <linux/hash.h>
+#include <linux/kthread.h>
void __init_waitqueue_head(wait_queue_head_t *q, const char *name, struct
lock_class_key *key)
{
@@ -297,6 +298,10 @@ int autoremove_wake_function(wait_queue_
}
EXPORT_SYMBOL(autoremove_wake_function);
+static inline bool is_kthread_should_stop(void)
+{
+ return (current->flags & PF_KTHREAD) && kthread_should_stop();
+}
/*
* DEFINE_WAIT_FUNC(wait, woken_wake_func);
@@ -326,7 +331,7 @@ long wait_woken(wait_queue_t *wait, unsi
* woken_wake_function() such that if we observe WQ_FLAG_WOKEN we must
* also observe all state before the wakeup.
*/
- if (!(wait->flags & WQ_FLAG_WOKEN))
+ if (!(wait->flags & WQ_FLAG_WOKEN) && !is_kthread_should_stop())
timeout = schedule_timeout(timeout);
__set_current_state(TASK_RUNNING);
--
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