[PATCH] x86_64: Fix mce_log
The attempt to fixup the lockless mce log buffer introduced an infinite loop
when trying to find a free entry.
And:
Using rcu_dereference() to load mcelog.next doesn't seem to be sufficient
enough to ensure that mcelog.next is loaded each time around the loop in
mce_log(). Instead, use an explicit rmb() to ensure that the compiler gets it
right.
AK: turned the smp_wmbs into true wmbs to make sure they are not
reordered by the compiler on UP.
Signed-off-by: Mike Waychison <mikew@google.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/arch/x86_64/kernel/mce.c b/arch/x86_64/kernel/mce.c
index 08203b0..69541db 100644
--- a/arch/x86_64/kernel/mce.c
+++ b/arch/x86_64/kernel/mce.c
@@ -54,9 +54,12 @@
{
unsigned next, entry;
mce->finished = 0;
- smp_wmb();
+ wmb();
for (;;) {
entry = rcu_dereference(mcelog.next);
+ /* The rmb forces the compiler to reload next in each
+ iteration */
+ rmb();
for (;;) {
/* When the buffer fills up discard new entries. Assume
that the earlier errors are the more interesting. */
@@ -69,6 +72,7 @@
entry++;
continue;
}
+ break;
}
smp_rmb();
next = entry + 1;
@@ -76,9 +80,9 @@
break;
}
memcpy(mcelog.entry + entry, mce, sizeof(struct mce));
- smp_wmb();
+ wmb();
mcelog.entry[entry].finished = 1;
- smp_wmb();
+ wmb();
if (!test_and_set_bit(0, &console_logged))
notify_user = 1;
