[PATCH -tip] x86, mce: CE in last bank prevents panic by unknownMCE

[Hidetoshi Seto]

[based on tip/x86/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 fix this undesired behavior, and clarify the logic.

Signed-off-by: Hidetoshi Seto <seto.hidetoshi@xxxxxxxxxxxxxx>
Reported-by: Jin Dongming <jin.dongming@xxxxxxxxxxxxxxxxxx>

---
 arch/x86/kernel/cpu/mcheck/mce.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index 54bd1b2..7b485e9 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c
@@ -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();
 
 	/*
-- 
1.6.4.1


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