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, 4 insertions, 6 deletions

diff --git a/arch/s390/kernel/topology.c b/arch/s390/kernel/topology.c
index fc957f2eef7c..80ca4ba759f6 100644
--- a/arch/s390/kernel/topology.c
+++ b/arch/s390/kernel/topology.c
@@ -251,12 +251,10 @@ static void update_cpu_core_map(void)
 
 void store_topology(struct sysinfo_15_1_x *info)
 {
-        int rc;
-
-        rc = stsi(info, 15, 1, 3);
-        if (rc != -ENOSYS)
-                return;
-        stsi(info, 15, 1, 2);
+        if (topology_max_mnest >= 3)
+                stsi(info, 15, 1, 3);
+        else
+                stsi(info, 15, 1, 2);
 }
 
 int arch_update_cpu_topology(void)