Commit 7644143c authored by Mike Waychison's avatar Mike Waychison Committed by Linus Torvalds
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[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: default avatarMike Waychison <mikew@google.com>
Signed-off-by: default avatarAndi Kleen <ak@suse.de>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 7d318d77
......@@ -54,9 +54,12 @@ void mce_log(struct mce *mce)
{
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 @@ void mce_log(struct mce *mce)
entry++;
continue;
}
break;
}
smp_rmb();
next = entry + 1;
......@@ -76,9 +80,9 @@ void mce_log(struct mce *mce)
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;
......
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