[patch] pi-futex: missing pi_waiters plist initialization

[Heiko Carstens]

From: Heiko Carstens <heiko.carstens@xxxxxxxxxx>

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@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
---

 kernel/sched.c |    5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/sched.c b/kernel/sched.c
index b44b9a4..db1014d 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6761,6 +6761,11 @@ #endif
 	}
 
 	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:
 	 */
-
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