[PATCH] Drop tasklist lock in do_sched_setscheduler

There is no need to hold tasklist_lock across the setscheduler call, when
we pin the task structure with get_task_struct().  Interrupts are disabled
in setscheduler anyway and the permission checks do not need interrupts
disabled.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

kernel/sched.c

@@ -4091,8 +4091,10 @@ do_sched_setscheduler(pid_t pid, int policy, struct sched_param __user *param)
 		read_unlock_irq(&tasklist_lock);
 		return -ESRCH;
 	}
-	retval = sched_setscheduler(p, policy, &lparam);
+	get_task_struct(p);
 	read_unlock_irq(&tasklist_lock);
+	retval = sched_setscheduler(p, policy, &lparam);
+	put_task_struct(p);
 	return retval;
 }