The patch titled
Fix a NO_IDLE_HZ timer bug
has been added to the -mm tree. Its filename is
fix-a-no_idle_hz-timer-bug.patch
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: Fix a NO_IDLE_HZ timer bug
From: Zachary Amsden <zach@xxxxxxxxxx>
Under certain timing conditions, a race during boot occurs where timer
ticks are being processed on remote CPUs. The remote timer ticks can
increment jiffies, and if this happens during a window when a timeout is
very close to expiring but a local tick has not yet been delivered, you can
end up with
1) No softirq pending
2) A local timer wheel which is not synced to jiffies
3) No high resolution timer active
4) A local timer which is supposed to fire before the current jiffies value.
In this circumstance, the comparison in next_timer_interrupt overflows,
because the base of the comparison for high resolution timers is jiffies,
but for the softirq timer wheel, it is relative the the current base of the
wheel (jiffies_base).
Signed-off-by: Zachary Amsden <zach@xxxxxxxxxx>
Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
kernel/timer.c | 16 ++++++++++++++++
1 files changed, 16 insertions(+)
diff -puN kernel/timer.c~fix-a-no_idle_hz-timer-bug kernel/timer.c
--- devel/kernel/timer.c~fix-a-no_idle_hz-timer-bug 2006-05-18 14:51:08.000000000 -0700
+++ devel-akpm/kernel/timer.c 2006-05-18 14:51:08.000000000 -0700
@@ -537,6 +537,22 @@ found:
}
spin_unlock(&base->lock);
+ /*
+ * It can happen that other CPUs service timer IRQs and increment
+ * jiffies, but we have not yet got a local timer tick to process
+ * the timer wheels. In that case, the expiry time can be before
+ * jiffies, but since the high-resolution timer here is relative to
+ * jiffies, the default expression when high-resolution timers are
+ * not active,
+ *
+ * time_before(MAX_JIFFY_OFFSET + jiffies, expires)
+ *
+ * would falsely evaluate to true. If that is the case, just
+ * return jiffies so that we can immediately fire the local timer
+ */
+ if (time_before(expires, jiffies))
+ return jiffies;
+
if (time_before(hr_expires, expires))
return hr_expires;
_
Patches currently in -mm which might be from zach@xxxxxxxxxx are
fix-a-no_idle_hz-timer-bug.patch
x86-cpu_init-avoid-gfp_kernel-allocation-while-atomic.patch
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