The patch titled
cpufreq: fix timer teardown in ondemand governor
has been added to the -mm tree. Its filename is
cpufreq-fix-timer-teardown-in-ondemand-governor.patch
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Subject: cpufreq: fix timer teardown in ondemand governor
From: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>
The problem is that dbs_timer_exit() uses cancel_delayed_work() when it
should use cancel_delayed_work_sync(). cancel_delayed_work() does not
wait for the workqueue handler to exit.
The ondemand governor does not "seem" to be affected (read : race
condition occurs very rarely) because the "if (!dbs_info->enable)" check
at the beginning of the workqueue handler returns immediately without
rescheduling the work. The conservative governor in 2.6.30-rc has the
same check as the ondemand governor, which makes things usually run
smoothly. However, if the governor is quickly stopped and then started,
this could lead to the following race :
dbs_enable could be reenabled and multiple do_dbs_timer handlers would
run. This is why a synchronized teardown is required.
The patch applies to, at least, 2.6.28.x, 2.6.29.1, 2.6.30-rc2.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>
Cc: Greg KH <greg@xxxxxxxxx>
Cc: <stable@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: "Rafael J. Wysocki" <rjw@xxxxxxx>,
Cc: Ben Slusky <sluskyb@xxxxxxxxxxxxxx>
Cc: Dave Jones <davej@xxxxxxxxxx>
Cc: Chris Wright <chrisw@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/cpufreq/cpufreq_ondemand.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff -puN drivers/cpufreq/cpufreq_ondemand.c~cpufreq-fix-timer-teardown-in-ondemand-governor drivers/cpufreq/cpufreq_ondemand.c
--- a/drivers/cpufreq/cpufreq_ondemand.c~cpufreq-fix-timer-teardown-in-ondemand-governor
+++ a/drivers/cpufreq/cpufreq_ondemand.c
@@ -98,6 +98,9 @@ static unsigned int dbs_enable; /* numbe
* (like __cpufreq_driver_target()) is being called with dbs_mutex taken, then
* cpu_hotplug lock should be taken before that. Note that cpu_hotplug lock
* is recursive for the same process. -Venki
+ * DEADLOCK ALERT! (2) : do_dbs_timer() must not take the dbs_mutex, because it
+ * would deadlock with cancel_delayed_work_sync(), which is needed for proper
+ * raceless workqueue teardown.
*/
static DEFINE_MUTEX(dbs_mutex);
@@ -562,7 +565,7 @@ static inline void dbs_timer_init(struct
static inline void dbs_timer_exit(struct cpu_dbs_info_s *dbs_info)
{
dbs_info->enable = 0;
- cancel_delayed_work(&dbs_info->work);
+ cancel_delayed_work_sync(&dbs_info->work);
}
static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
_
Patches currently in -mm which might be from mathieu.desnoyers@xxxxxxxxxx are
linux-next.patch
cpufreq-fix-timer-teardown-in-conservative-governor-2630-rc2.patch
cpufreq-fix-timer-teardown-in-ondemand-governor.patch
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