From 7644143cd6f7e029f3a8ea64f5fb0ab33ec39f72 Mon Sep 17 00:00:00 2001 From: Mike Waychison Date: Fri, 30 Sep 2005 00:01:27 +0200 Subject: [PATCH] [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 Signed-off-by: Andi Kleen Signed-off-by: Linus Torvalds --- arch/x86_64/kernel/mce.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) diff --git a/arch/x86_64/kernel/mce.c b/arch/x86_64/kernel/mce.c index 08203b07f4bd..69541db5ff2c 100644 --- a/arch/x86_64/kernel/mce.c +++ b/arch/x86_64/kernel/mce.c @@ -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;