[PATCH] pi-futex: missing pi_waiters plist initialization

Initialize init task's pi_waiters plist.  Otherwise cpu hotplug of cpu 0
might crash, since rt_mutex_getprio() accesses an uninitialized list head.

call chain which led to crash:

take_cpu_down
sched_idle_next
__setscheduler
rt_mutex_getprio

Using PLIST_HEAD_INIT in the INIT_TASK macro doesn't work unfortunately,
since the pi_waiters member is only conditionally present.

Cc: Arjan van de Ven <arjan@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/kernel/sched.c b/kernel/sched.c
index de440b2..a2be2d0 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6766,6 +6766,11 @@ void __init sched_init(void)
        }
 
        set_load_weight(&init_task);
+
+#ifdef CONFIG_RT_MUTEXES
+       plist_head_init(&init_task.pi_waiters, &init_task.pi_lock);
+#endif
+
        /*
         * The boot idle thread does lazy MMU switching as well:
         */