[PATCH] - sys_sched_getaffinity & hotplug

[Jack Steiner <steiner@sgi.com>]

Change sched_getaffinity() so that it returns a bitmap that indicates the
legally schedulable cpus that a task is allowed to run on. 

Without this patch, if CONFIG_HOTPLUG_CPU is enabled, sched_getaffinity()
unconditionally returns (at least on IA64) a mask with NR_CPUS bits set.
This conveys no useful infornmation except for a kernel compile option.


	Signed-off-by: Jack Steiner <steiner@sgi.com>
	Acked-by: Ingo Molnar <mingo@elte.hu>

---
This fixes a breakage we obseved running recent kernels. We have MPI jobs
that use sched_getaffinity() to determine where to place their threads. 
Placing them on non-existant cpus is problematic :-)


Index: linux/kernel/sched.c
===================================================================
--- linux.orig/kernel/sched.c	2006-01-28 10:13:01.834293691 -0600
+++ linux/kernel/sched.c	2006-01-29 07:15:11.217227453 -0600
@@ -4031,7 +4031,7 @@ long sched_getaffinity(pid_t pid, cpumas
 		goto out_unlock;
 
 	retval = 0;
-	cpus_and(*mask, p->cpus_allowed, cpu_possible_map);
+	cpus_and(*mask, p->cpus_allowed, cpu_online_map);
 
 out_unlock:
 	read_unlock(&tasklist_lock);