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Commit 673242c1 authored by Andi Kleen's avatar Andi Kleen Committed by Linus Torvalds
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[PATCH] x86-64: Make lockless machine check record passing a bit more robust. 



One machine is constantly throwing NMI watchdog timeouts in mce_log

This was one attempt to fix it.

(AK: this doesn't actually fix the bug I'm seeing unfortunately, probably
drop.  I don't like it that the reader can spin forever now waiting
for a writer)

Signed-off-by: default avatarAndi Kleen <ak@suse.de>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent a54e678b

arch/x86_64/kernel/mce.c

+21 −11
Original line number Diff line number Diff line
@@ -56,6 +56,7 @@ void mce_log(struct mce *mce) 
	smp_wmb();

	for (;;) {

		entry = rcu_dereference(mcelog.next);

		for (;;) {

			/* When the buffer fills up discard new entries. Assume

			   that the earlier errors are the more interesting. */

			if (entry >= MCE_LOG_LEN) {
@@ -63,8 +64,11 @@ void mce_log(struct mce *mce) 
				return;

			}

			/* Old left over entry. Skip. */

		if (mcelog.entry[entry].finished)

			if (mcelog.entry[entry].finished) {

				entry++;

				continue;

			}

		}

		smp_rmb();

		next = entry + 1;

		if (cmpxchg(&mcelog.next, entry, next) == entry)
@@ -405,8 +409,14 @@ static ssize_t mce_read(struct file *filp, char __user *ubuf, size_t usize, loff 


	err = 0;

	for (i = 0; i < next; i++) {		

		if (!mcelog.entry[i].finished)

		unsigned long start = jiffies;

		while (!mcelog.entry[i].finished) {

			if (!time_before(jiffies, start + 2)) {

				memset(mcelog.entry + i,0, sizeof(struct mce));

				continue;

			}

			cpu_relax();

		}

		smp_rmb();

		err |= copy_to_user(buf, mcelog.entry + i, sizeof(struct mce));

		buf += sizeof(struct mce);