x86, mce: CE in last bank prevents panic by unknown MCE

If MCE handler is called but none of mces_seen have machine
check event which might signal the MCE (i.e. event higher than
MCE_KEEP_SEVERITY), panic with "Machine check from unknown
source" will be taken since the MCE is assumed to be signaled
from external agent or so.

Usually mces_seen never point MCE_KEEP_SEVERITY event such as
CE. But it can happen because initial value of mces_seen is
accidentally modified by mce_no_way_out() - in case if
mce_no_way_out() run through all banks and the last bank has
the CE, mces_seen points the CE and the "panic by unknown" will
not be taken.

This patch fixes this undesired behavior, and clarifies the logic.

Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jin Dongming <jin.dongming@np.css.fujitsu.com>
LKML-Reference: <4A94E244.3020301@jp.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Reported-by: Jin Dongming <jin.dongming@np.css.fujitsu.com>

1 files changed, 4 insertions, 4 deletions

diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index 54bd1b2fb4c..325559d1aa5 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -612,7 +612,7 @@ out:
  * This way we prevent any potential data corruption in a unrecoverable case
  * and also makes sure always all CPU's errors are examined.
  *
- * Also this detects the case of an machine check event coming from outer
+ * Also this detects the case of a machine check event coming from outer
  * space (not detected by any CPUs) In this case some external agent wants
  * us to shut down, so panic too.
  *
@@ -665,7 +665,7 @@ static void mce_reign(void)
          * No machine check event found. Must be some external
          * source or one CPU is hung. Panic.
          */
-        if (!m && tolerant < 3)
+        if (global_worst <= MCE_KEEP_SEVERITY && tolerant < 3)
                 mce_panic("Machine check from unknown source", NULL, NULL);
 
         /*
@@ -889,11 +889,11 @@ void do_machine_check(struct pt_regs *regs, long error_code)
         mce_setup(&m);
 
         m.mcgstatus = mce_rdmsrl(MSR_IA32_MCG_STATUS);
-        no_way_out = mce_no_way_out(&m, &msg);
-
         final = &__get_cpu_var(mces_seen);
         *final = m;
 
+        no_way_out = mce_no_way_out(&m, &msg);
+
         barrier();
 
         /*