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[PATCH] x86_64: Fix mce_log

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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>
This commit is contained in:
Mike Waychison 2005-09-30 00:01:27 +02:00 committed by Linus Torvalds
parent 7d318d7747
commit 7644143cd6
1 changed files with 7 additions and 3 deletions
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10
arch/x86_64/kernel/mce.c
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@ -54,9 +54,12 @@ void mce_log(struct mce *mce)
{ {
unsigned next, entry; unsigned next, entry;
mce->finished = 0; mce->finished = 0;
smp_wmb(); wmb();
for (;;) { for (;;) {
entry = rcu_dereference(mcelog.next); entry = rcu_dereference(mcelog.next);
/* The rmb forces the compiler to reload next in each
iteration */
rmb();
for (;;) { for (;;) {
/* When the buffer fills up discard new entries. Assume /* When the buffer fills up discard new entries. Assume
that the earlier errors are the more interesting. */ that the earlier errors are the more interesting. */
@ -69,6 +72,7 @@ void mce_log(struct mce *mce)
entry++; entry++;
continue; continue;
} }
break;
} }
smp_rmb(); smp_rmb();
next = entry + 1; next = entry + 1;
@ -76,9 +80,9 @@ void mce_log(struct mce *mce)
break; break;
} }
memcpy(mcelog.entry + entry, mce, sizeof(struct mce)); memcpy(mcelog.entry + entry, mce, sizeof(struct mce));
smp_wmb(); wmb();
mcelog.entry[entry].finished = 1; mcelog.entry[entry].finished = 1;
smp_wmb(); wmb();
if (!test_and_set_bit(0, &console_logged)) if (!test_and_set_bit(0, &console_logged))
notify_user = 1; notify_user = 1;