tree 3371de51ff061cde22dc824f83f4a66c7701dc67
parent d8aaf12142d066d3982475d58a9094c85a06a5a9
author Joshua Wise <jwise@google.com> 1182644205 -0700
committer Linus Torvalds <torvalds@woody.linux-foundation.org> 1182700752 -0700

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>