[PATCH 4/7] audit,wait: Fixup kauditd_thread wait loop

From: Peter Zijlstra
Date: Fri Oct 31 2014 - 07:23:11 EST


The kauditd_thread wait loop is a bit iffy; it has a number of problems:

- calls try_to_freeze() before schedule(); you typically want the
thread to re-evaluate the sleep condition when unfreezing, also
freeze_task() issues a wakeup.

- it unconditionally does the {add,remove}_wait_queue(), even when the
sleep condition is false.

Use wait_event_freezable() that does the right thing.

Cc: mingo@xxxxxxxxxx
Cc: oleg@xxxxxxxxxx
Cc: torvalds@xxxxxxxxxxxxxxxxxxxx
Cc: tglx@xxxxxxxxxxxxx
Cc: Eric Paris <eparis@xxxxxxxxxx>
Reported-by: Mike Galbraith <umgwanakikbuti@xxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/20141002102251.GA6324@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
---
kernel/audit.c | 11 +----------
1 file changed, 1 insertion(+), 10 deletions(-)

--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -499,7 +499,6 @@ static int kauditd_thread(void *dummy)
set_freezable();
while (!kthread_should_stop()) {
struct sk_buff *skb;
- DECLARE_WAITQUEUE(wait, current);

flush_hold_queue();

@@ -514,16 +513,8 @@ static int kauditd_thread(void *dummy)
audit_printk_skb(skb);
continue;
}
- set_current_state(TASK_INTERRUPTIBLE);
- add_wait_queue(&kauditd_wait, &wait);

- if (!skb_queue_len(&audit_skb_queue)) {
- try_to_freeze();
- schedule();
- }
-
- __set_current_state(TASK_RUNNING);
- remove_wait_queue(&kauditd_wait, &wait);
+ wait_event_freezable(kauditd_wait, skb_queue_len(&audit_skb_queue));
}
return 0;
}


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