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authorZachary Amsden <zach@vmware.com>2006-05-20 15:00:24 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2006-05-21 12:59:21 -0700
commit0662b71322e211dba9a4bc0e6fbca7861a2b5a7d (patch)
treebffce074929b6a36b7b1e00a485df7a5fe95cc22 /kernel
parent[PATCH] missing newline in scsi/st.c (diff)
downloadlinux-dev-0662b71322e211dba9a4bc0e6fbca7861a2b5a7d.tar.xz
linux-dev-0662b71322e211dba9a4bc0e6fbca7861a2b5a7d.zip
[PATCH] Fix a NO_IDLE_HZ timer bug
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@vmware.com> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Oleg Nesterov <oleg@tv-sign.ru> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/timer.c16
1 files changed, 16 insertions, 0 deletions
diff --git a/kernel/timer.c b/kernel/timer.c
index 67eaf0f54096..9e49deed468c 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -541,6 +541,22 @@ 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;