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Replace my previous patch with equivalent fix from linux-2.6.17.
Might as well stay as close to that as we can... Signed-off-by: Emmanuel Ackaouy <ack@xensource.com>
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+18
-14
@@ -1,22 +1,26 @@
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diff -pruN ../pristine-linux-2.6.16.13/kernel/timer.c ./kernel/timer.c
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--- ../pristine-linux-2.6.16.13/kernel/timer.c 2006-05-02 14:38:44.000000000 -0700
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+++ ./kernel/timer.c 2006-06-28 09:57:51.000000000 -0700
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@@ -555,7 +555,17 @@ found:
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--- ../pristine-linux-2.6.16.13/kernel/timer.c 2006-05-02 22:38:44.000000000 +0100
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+++ ./kernel/timer.c 2006-06-29 14:34:12.788957720 +0100
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@@ -555,6 +555,22 @@ found:
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}
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spin_unlock(&base->t_base.lock);
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- if (time_before(hr_expires, expires))
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+ /*
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+ * If timers are pending, "expires" will be in the recent past
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+ * of "jiffies". If there are no hr_timers registered, "hr_expires"
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+ * will be "jiffies + MAX_JIFFY_OFFSET"; this is *just* short of being
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+ * considered to be before "jiffies". This makes it very likely that
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+ * "hr_expires" *will* be considered to be before "expires".
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+ * So we must check when there are pending timers (expires <= jiffies)
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+ * to ensure that we don't accidently tell the caller that there is
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+ * nothing scheduled until half an epoch (MAX_JIFFY_OFFSET)!
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+ * It can happen that other CPUs service timer IRQs and increment
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+ * jiffies, but we have not yet got a local timer tick to process
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+ * the timer wheels. In that case, the expiry time can be before
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+ * jiffies, but since the high-resolution timer here is relative to
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+ * jiffies, the default expression when high-resolution timers are
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+ * not active,
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+ *
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+ * time_before(MAX_JIFFY_OFFSET + jiffies, expires)
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+ *
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+ * would falsely evaluate to true. If that is the case, just
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+ * return jiffies so that we can immediately fire the local timer
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+ */
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+ if (time_before(jiffies, expires) && time_before(hr_expires, expires))
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+ if (time_before(expires, jiffies))
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+ return jiffies;
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+
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if (time_before(hr_expires, expires))
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return hr_expires;
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return expires;
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