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SubjectDriver snd-hrtimer - causing system freeze with Rosegarden
When I try to use the "HR timer" as a MIDI sequencer timer in the
Rosegarden ( application, the system
freezes. Another people also reported similar problems with other
sequencer - OpenOctave ( )

I have tested the problem on two SMP machines with diffrent kernels
(2.6.30,, 2.6.32).
The problem seems to be associated with the "snd-hrtimer" module.
I've tried to run the application vie remote X session, while having the
text console active.
Before the machine froze, the following messages have been displayed in
the console:

System 1 (Intel(R) Pentium(R) 4 CPU 2.80GHz HT)

hrtimer: interrupt too slow, forcing clock min delta to 3568 ns

System 2 (Intel(R) Core(TM)2 CPU T5500 @ 1.66GHz)
hrtimer: interrupt too slow, forcing clock min delta to 11103 ns
CE: hpet increasing min_delta_ns to 15000 nsec
CE: hpet increasing min_delta_ns to 22500 nsec
CE: hpet increasing min_delta_ns to 33750 nsec

Analyzing the problem, I had an idea, that maybe the snd-hrtimer should
be rewritten to call
the callback via tasklet (I attach my patch only as an ilustration, my
code doesn't work either),
however then I got the message "BUG: scheduling while atomic" or
something like this
from the snd_hrtimer_stop function called from _snd_timer_stop.
Therefore I've tried to investigate the snd_hrtimer_stop more thoroughly.

Looking further into the code, I have found, that snd_hrtimer_stop may
be called
from the callback routine (e.g.: or )

It seems to me, that calling hrtimer_cancel (in the original code),
which waits for the handler to finish,
from that handler may lock the machine...
(snd_hrtimer_callback calls the snd_timer_interrupt:
which in turn calls snd_hrtimer_stop (as above) which calls hrtimer_cancel).

Unfortunately currently I have no idea how to fix this problem. Maybe
snd_hrtimer_stop shouldn't try to cancel the timer,
instead setting a flag causing callback to return immediately without
rearming of the timer?

Best regards,
Wojtek Zabolotny

--- hrtimer.c 2009-11-10 01:32:31.000000000 +0100
+++ /tmp/hrtimer.c 2009-12-09 19:10:34.000000000 +0100
@@ -36,12 +36,13 @@

struct snd_hrtimer {
struct snd_timer *timer;
- struct hrtimer hrt;
+ struct tasklet_hrtimer thrt;

static enum hrtimer_restart snd_hrtimer_callback(struct hrtimer *hrt)
- struct snd_hrtimer *stime = container_of(hrt, struct snd_hrtimer, hrt);
+ struct tasklet_hrtimer *thrt = container_of(hrt, struct tasklet_hrtimer, timer);
+ struct snd_hrtimer *stime = container_of(thrt, struct snd_hrtimer, thrt);
struct snd_timer *t = stime->timer;
hrtimer_forward_now(hrt, ns_to_ktime(t->sticks * resolution));
snd_timer_interrupt(stime->timer, t->sticks);
@@ -55,9 +56,8 @@
stime = kmalloc(sizeof(*stime), GFP_KERNEL);
if (!stime)
return -ENOMEM;
- hrtimer_init(&stime->hrt, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+ tasklet_hrtimer_init(&stime->thrt, snd_hrtimer_callback, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
stime->timer = t;
- stime->hrt.function = snd_hrtimer_callback;
t->private_data = stime;
return 0;
@@ -67,7 +67,7 @@
struct snd_hrtimer *stime = t->private_data;

if (stime) {
- hrtimer_cancel(&stime->hrt);
+ tasklet_hrtimer_cancel(&stime->thrt);
t->private_data = NULL;
@@ -78,7 +78,7 @@
struct snd_hrtimer *stime = t->private_data;

- hrtimer_start(&stime->hrt, ns_to_ktime(t->sticks * resolution),
+ tasklet_hrtimer_start(&stime->thrt, ns_to_ktime(t->sticks * resolution),
return 0;
@@ -87,12 +87,14 @@
struct snd_hrtimer *stime = t->private_data;

- hrtimer_cancel(&stime->hrt);
+ tasklet_hrtimer_cancel(&stime->thrt);
return 0;

static struct snd_timer_hardware hrtimer_hw = {
+ .flags = SNDRV_TIMER_HW_AUTO |\
.open = snd_hrtimer_open,
.close = snd_hrtimer_close,
.start = snd_hrtimer_start,
 \ /
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