s390/sysinfo,topology: fix cpu topology maximum nesting detection

The maximum nesting of the cpu topology is evaluated when /proc/sysinfo
is the first time read. This happens without a lock and a concurrent
reader on a different cpu can see and use an invalid intermediate value.
Besides the fact that this race is quite unlikely the worst thing that
could happen is that /proc/sysinfo would contain bogus information about
the machine's cpu topology.
Nevertheless this should be fixed. So move the detection code to the
early machine detection code and since now the value is early available
use it in the topology code as well.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 3 insertions, 9 deletions

diff --git a/arch/s390/kernel/sysinfo.c b/arch/s390/kernel/sysinfo.c
index 2249b0cf80ef..2af4ee67fe52 100644
--- a/arch/s390/kernel/sysinfo.c
+++ b/arch/s390/kernel/sysinfo.c
@@ -22,6 +22,8 @@
 #include <math-emu/soft-fp.h>
 #include <math-emu/single.h>
 
+int topology_max_mnest;
+
 static inline int stsi_0(void)
 {
 	int rc = stsi(NULL, 0, 0, 0);
@@ -95,15 +97,7 @@ static void stsi_15_1_x(struct seq_file *m, struct sysinfo_15_1_x *info)
 	seq_putc(m, '\n');
 	if (!MACHINE_HAS_TOPOLOGY)
 		return;
-	if (max_mnest) {
-		stsi(info, 15, 1, max_mnest);
-	} else {
-		for (max_mnest = 6; max_mnest > 1; max_mnest--) {
-			rc = stsi(info, 15, 1, max_mnest);
-			if (rc != -ENOSYS)
-				break;
-		}
-	}
+	stsi(info, 15, 1, topology_max_mnest);
 	seq_printf(m, "CPU Topology HW:     ");
 	for (i = 0; i < TOPOLOGY_NR_MAG; i++)
 		seq_printf(m, " %d", info->mag[i]);