[PATCH] cpumask: range check before using value

When setting the 'cpu_isolated_map' mask, check that the user input value
is valid (in range 0 ..  NR_CPUS - 1).  Also fix up kernel-parameters.txt
for this parameter.
Signed-off-by: Randy Dunlap <rddunlap@osdl.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

Documentation/kernel-parameters.txt

@@ -587,11 +587,13 @@ running once the system is up.
 			Format: <RDP>, <reset>, <pci_scan>, <verbosity>
 
 	isolcpus=	[KNL,SMP] Isolate CPUs from the general scheduler.
-			Format: <cpu number>, ..., <cpu number>
+			Format: <cpu number>,...,<cpu number>
 			This option can be used to specify one or more CPUs
 			to isolate from the general SMP balancing and scheduling
 			algorithms. The only way to move a process onto or off
 			an "isolated" CPU is via the CPU affinity syscalls.
+			<cpu number> begins at 0 and the maximum value is
+			"number of CPUs in system - 1".
 
 			This option is the preferred way to isolate CPUs. The
 			alternative - manually setting the CPU mask of all tasks

kernel/sched.c

@@ -36,6 +36,7 @@
 #include <linux/blkdev.h>
 #include <linux/delay.h>
 #include <linux/smp.h>
+#include <linux/threads.h>
 #include <linux/timer.h>
 #include <linux/rcupdate.h>
 #include <linux/cpu.h>
@@ -4169,7 +4170,8 @@ static int __init isolated_cpu_setup(char *str)
 	str = get_options(str, ARRAY_SIZE(ints), ints);
 	cpus_clear(cpu_isolated_map);
 	for (i = 1; i <= ints[0]; i++)
-		cpu_set(ints[i], cpu_isolated_map);
+		if (ints[i] < NR_CPUS)
+			cpu_set(ints[i], cpu_isolated_map);
 	return 1;
 }