freezer: fix kthread_create vs freezer theoretical race

kthread() sleeps in TASK_INTERRUPTIBLE state waiting for the first wakeup.  In
theory, this wakeup may come from freeze_process()->signal_wake_up(), so the
task can disappear even before kthread_create() sets its ->comm.

Change kthread() to use TASK_UNINTERRUPTIBLE.

[akpm@linux-foundation.org: s/BUG_ON/WARN_ON+recover]
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Cc: Gautham R Shenoy <ego@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 2 deletions

diff --git a/kernel/kthread.c b/kernel/kthread.c
index df8a8e8f6ca4..bbd51b81a3e8 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -70,7 +70,7 @@ static int kthread(void *_create)
         data = create->data;
 
         /* OK, tell user we're spawned, wait for stop or wakeup */
-        __set_current_state(TASK_INTERRUPTIBLE);
+        __set_current_state(TASK_UNINTERRUPTIBLE);
         complete(&create->started);
         schedule();
 
@@ -162,7 +162,10 @@ EXPORT_SYMBOL(kthread_create);
  */
 void kthread_bind(struct task_struct *k, unsigned int cpu)
 {
-        BUG_ON(k->state != TASK_INTERRUPTIBLE);
+        if (k->state != TASK_UNINTERRUPTIBLE) {
+                WARN_ON(1);
+                return;
+        }
         /* Must have done schedule() in kthread() before we set_task_cpu */
         wait_task_inactive(k);
         set_task_cpu(k, cpu);