If this thread is preempted at(or before) location a, and the other thread
set the condition followed with wake_up_process. After that
when this thread is re-scheduled, calling set_current_state to set itself as
state TASK_UNINTERRUPTIBLE, if it is preempted again after that and before
__set_current_state(TASK_RUNNING), it triggers the invalid wakeup problem.
----------------
wait_for_auditd()
----------------
...
//location a
set_current_state(TASK_UNINTERRUPTIBLE);
...
if (audit_backlog_limit &&
skb_queue_len(&audit_skb_queue) > audit_backlog_limit)
//location b
schedule_timeout(sleep_time);
//location c
__set_current_state(TASK_RUNNING);
//location d
...
To solve this problem, using preempt_disable() to bound the operaion that
setting the task state and the conditions(set by the wake thread) validation.
----------------
wait_for_auditd()
----------------
...
preempt_disable();
set_current_state(TASK_UNINTERRUPTIBLE);
...
if (audit_backlog_limit &&
skb_queue_len(&audit_skb_queue) > audit_backlog_limit) {
preempt_enable();
schedule_timeout(sleep_time);
preempt_disable();
}
__set_current_state(TASK_RUNNING);
preempt_enable();
...
Signed-off-by: Libin <[email protected]>
---
kernel/audit.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/kernel/audit.c b/kernel/audit.c
index a7d1346..48d2f76 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -1060,14 +1060,19 @@ static inline void audit_get_stamp(struct audit_context
*ctx,
static void wait_for_auditd(unsigned long sleep_time)
{
DECLARE_WAITQUEUE(wait, current);
+ preempt_disable();
set_current_state(TASK_UNINTERRUPTIBLE);
add_wait_queue(&audit_backlog_wait, &wait);
if (audit_backlog_limit &&
- skb_queue_len(&audit_skb_queue) > audit_backlog_limit)
+ skb_queue_len(&audit_skb_queue) > audit_backlog_limit) {
+ preempt_enable();
schedule_timeout(sleep_time);
+ preempt_disable();
+ }
__set_current_state(TASK_RUNNING);
+ preempt_enable();
remove_wait_queue(&audit_backlog_wait, &wait);
}
--
1.8.2.1
--
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