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

arch/x86_64/kernel/mce.c

+7 −3
Original line number Diff line number Diff line
@@ -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;