diff options
authorJoshua Wise <jwise@google.com>2007-06-23 17:16:45 -0700
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-06-24 08:59:12 -0700
commit4f84e4be53a04a65d97bf0faa0c8f99e29bc0170 (patch)
parentd8aaf12142d066d3982475d58a9094c85a06a5a9 (diff)
x86_64: fix misplaced `continue' in mce.c
Background: When a userspace application wants to know about machine check events, it opens /dev/mcelog and does a read(). Usually, we found that this interface works well, but in some cases, when the system was taking large numbers of machine check exceptions, the read() would hang. The system would output a soft-lockup warning, and the daemon reading from /dev/mcelog would suck up as much of a single CPU as it could spinning in system space. Description: This patch fixes this bug. In particular, there was a "continue" inside a timeout loop that presumably was intended to break out of the outer loop, but instead caused the inner loop to continue. This patch also makes the condition for the break-out a little more evident by changing a !time_before to a time_after_eq. Result: The read() no longer hangs in this test case. Testing: On my system, I could replicate the bug with the following command: # for i in `seq 15000`; do ./inject_sbe.sh; done where inject_sbe.sh contains commands to inject a single-bit error into the next memory write transaction. Patch: This patch is against git f1518a088bde6aea49e7c472ed6ab96178fcba3e. Signed-off-by: Joshua Wise <jwise@google.com> Signed-off-by: Tim Hockin <thockin@google.com> Cc: Andi Kleen <ak@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 files changed, 4 insertions, 2 deletions
diff --git a/arch/x86_64/kernel/mce.c b/arch/x86_64/kernel/mce.c
index a14375dd5425..aa1d15991794 100644
--- a/arch/x86_64/kernel/mce.c
+++ b/arch/x86_64/kernel/mce.c
@@ -497,15 +497,17 @@ static ssize_t mce_read(struct file *filp, char __user *ubuf, size_t usize, loff
for (i = 0; i < next; i++) {
unsigned long start = jiffies;
while (!mcelog.entry[i].finished) {
- if (!time_before(jiffies, start + 2)) {
+ if (time_after_eq(jiffies, start + 2)) {
memset(mcelog.entry + i,0, sizeof(struct mce));
- continue;
+ goto timeout;
err |= copy_to_user(buf, mcelog.entry + i, sizeof(struct mce));
buf += sizeof(struct mce);
+ timeout:
+ ;
memset(mcelog.entry, 0, next * sizeof(struct mce));