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SubjectRe: [ANNOUNCE] 2.6.15-rc5-hrt2 - hrtimers based high resolution patches
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Thomas and Ingo,

I found a bug in 2.6.15-rc5-rt1 that was due to a race in the hrtimers
code. This bug is most likely in the vanilla hrtimers code as well.

I added a HRTIMER_RUNNING state because there's a moment in the
run_hrtimer_queues that turns interrupts on and releases the base lock.
In this time, a remove_hrtimer can be called while the state is still
HRTIMER_PENDING_CALLBACK, but it has been removed off the list. The
remove_hrtimer will then try to remove this again.

Since I couldn't think of which state to use, I created the
HRTIMER_RUNNING, and used that instead.

I have a program (a simple jitter test) that, with out the patch,
reliably crashes the 2.6.15-rc5-rt1 on a slow UP machine. With the
patch, it runs solidly, so I know this is the reason for the crash.

-- Steve

Index: linux-2.6.15-rc5-rt1/kernel/hrtimer.c
===================================================================
--- linux-2.6.15-rc5-rt1.orig/kernel/hrtimer.c 2005-12-13 15:51:52.000000000 -0500
+++ linux-2.6.15-rc5-rt1/kernel/hrtimer.c 2005-12-13 15:53:36.000000000 -0500
@@ -846,6 +846,7 @@
data = timer->data;
set_curr_timer(base, timer);
list_del(&timer->list);
+ timer->state = HRTIMER_RUNNING;
spin_unlock_irq(&base->lock);

/*
@@ -904,6 +905,7 @@
data = timer->data;
set_curr_timer(base, timer);
__remove_hrtimer(timer, base);
+ timer->state = HRTIMER_RUNNING;
spin_unlock_irq(&base->lock);

/*
Index: linux-2.6.15-rc5-rt1/include/linux/hrtimer.h
===================================================================
--- linux-2.6.15-rc5-rt1.orig/include/linux/hrtimer.h 2005-12-13 15:51:40.000000000 -0500
+++ linux-2.6.15-rc5-rt1/include/linux/hrtimer.h 2005-12-13 15:55:21.000000000 -0500
@@ -41,6 +41,7 @@
enum hrtimer_state {
HRTIMER_INACTIVE, /* Timer is inactive */
HRTIMER_EXPIRED, /* Timer is expired */
+ HRTIMER_RUNNING, /* Timer is currently running */
HRTIMER_PENDING, /* Timer is pending */
HRTIMER_PENDING_CALLBACK, /* Timer is expired, callback pending */
};

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