Merge branch 'stable-3.2' into pandora-3.2

[pandora-kernel.git] / kernel / exit.c

diff --git a/kernel/exit.c b/kernel/exit.c
index 0eca2ef..7dcaf2e 100644 (file)
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1021,6 +1021,22 @@ NORET_TYPE void do_exit(long code)
 
        preempt_disable();
        exit_rcu();
+
+       /*
+        * The setting of TASK_RUNNING by try_to_wake_up() may be delayed
+        * when the following two conditions become true.
+        *   - There is race condition of mmap_sem (It is acquired by
+        *     exit_mm()), and
+        *   - SMI occurs before setting TASK_RUNINNG.
+        *     (or hypervisor of virtual machine switches to other guest)
+        *  As a result, we may become TASK_RUNNING after becoming TASK_DEAD
+        *
+        * To avoid it, we have to wait for releasing tsk->pi_lock which
+        * is held by try_to_wake_up()
+        */
+       smp_mb();
+       raw_spin_unlock_wait(&tsk->pi_lock);
+
        /* causes final put_task_struct in finish_task_switch(). */
        tsk->state = TASK_DEAD;
        schedule();