audit, sched/wait: Fixup kauditd_thread() wait loop

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.

Reported-by: Mike Galbraith <umgwanakikbuti@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Eric Paris <eparis@redhat.com>
Cc: oleg@redhat.com
Cc: Eric Paris <eparis@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20141002102251.GA6324@worktop.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/audit.c b/kernel/audit.c
index 80983df92cd441f981090394252126fbde22cd64..32bfc43ffb9a75b425a771496fae5c21e148c0a3 100644 (file)
--- 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;
 }