[PATCH 2/2] sched: Check if lowest_mask is initialized in find_lowest_rq

[Steven Rostedt <rostedt@goodmis.org>]

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From: Steven Rostedt <rostedt@goodmis.org>

On system boot up, the lowest_mask is initialized with early_initcall.
But RT tasks may wake up on other early_initcall callers before the
lowest_mask is initialized, causing a system crash.

The commit d72bce0e67 rcu: Cure load woes
was the first commit to wake up RT tasks in early init. Before this
commit this bug should not happen.

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Reported-by: Andrew Theurer <habanero@linux.vnet.ibm.com>
Tested-by: Andrew Theurer <habanero@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/1308014683.9218.107.camel@gandalf.stny.rr.com
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/sched_rt.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 9b8d5dc..10d0182 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -1239,6 +1239,10 @@ static int find_lowest_rq(struct task_struct *task)
 	int this_cpu = smp_processor_id();
 	int cpu      = task_cpu(task);
 
+	/* Make sure the mask is initialized first */
+	if (unlikely(!lowest_mask))
+		return -1;
+
 	if (task->rt.nr_cpus_allowed == 1)
 		return -1; /* No other targets possible */
 
-- 
1.7.4.4