Messages in this thread Patch in this message | | | Date | Thu, 21 Jun 2007 17:13:49 -0700 (PDT) | From | Joshua Wise <> | Subject | [PATCH] x86_64: Fix misplaced `continue' in mce.c |
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From: Joshua Wise <jwise@google.com>
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>
--
diff --git a/arch/x86_64/kernel/mce.c b/arch/x86_64/kernel/mce.c index a14375d..aa83023 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 *fil 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; } cpu_relax(); } smp_rmb(); err |= copy_to_user(buf, mcelog.entry + i, sizeof(struct mce)); buf += sizeof(struct mce); + timeout: + ; }
memset(mcelog.entry, 0, next * sizeof(struct mce)); - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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