>>> On 08.03.18 at 11:26, <mar...@c-home.cz> wrote:
> Console output added (7x OK, 2x FAILED).
Thanks. You've chopped off some of the messages though. I think
I've spotted the issue nevertheless - would you please give the
patch below a try?
Jan
cpufreq/ondemand: fix race while offlining CPU
Offlining a CPU involves stopping the cpufreq governor. The on-demand
governor will kill the timer before letting generic code proceed, but
since that generally isn't happening on the subject CPU,
cpufreq_dbs_timer_resume() may run in parallel. If that managed to
invoke the timer handler, that handler needs to run to completion before
dbs_timer_exit() may safely exit.
Make the "stoppable" field a tristate, changing it from +1 to -1 around
the timer function invocation, and make dbs_timer_exit() wait for it to
become non-negative (still writing zero if it's +1).
Also adjust coding style in cpufreq_dbs_timer_resume().
Reported-by: Martin Cerveny <mar...@c-home.cz>
Signed-off-by: Jan Beulich <jbeul...@suse.com>
--- unstable.orig/xen/drivers/cpufreq/cpufreq_ondemand.c
+++ unstable/xen/drivers/cpufreq/cpufreq_ondemand.c
@@ -204,7 +204,14 @@ static void dbs_timer_init(struct cpu_db
static void dbs_timer_exit(struct cpu_dbs_info_s *dbs_info)
{
dbs_info->enable = 0;
- dbs_info->stoppable = 0;
+
+ /*
+ * The timer function may be running (from cpufreq_dbs_timer_resume) -
+ * wait for it to complete.
+ */
+ while ( cmpxchg(&dbs_info->stoppable, 1, 0) < 0 )
+ cpu_relax();
+
kill_timer(&per_cpu(dbs_timer, dbs_info->cpu));
}
@@ -369,23 +376,22 @@ void cpufreq_dbs_timer_suspend(void)
void cpufreq_dbs_timer_resume(void)
{
- int cpu;
- struct timer* t;
- s_time_t now;
-
- cpu = smp_processor_id();
+ unsigned int cpu = smp_processor_id();
+ int8_t *stoppable = &per_cpu(cpu_dbs_info, cpu).stoppable;
- if ( per_cpu(cpu_dbs_info,cpu).stoppable )
+ if ( *stoppable )
{
- now = NOW();
- t = &per_cpu(dbs_timer, cpu);
- if (t->expires <= now)
+ s_time_t now = NOW();
+ struct timer *t = &per_cpu(dbs_timer, cpu);
+
+ if ( t->expires <= now )
{
+ if ( !cmpxchg(stoppable, 1, -1) )
+ return;
t->function(t->data);
+ (void)cmpxchg(stoppable, -1, 1);
}
else
- {
- set_timer(t, align_timer(now , dbs_tuners_ins.sampling_rate));
- }
+ set_timer(t, align_timer(now, dbs_tuners_ins.sampling_rate));
}
}
--- unstable.orig/xen/include/acpi/cpufreq/cpufreq.h
+++ unstable/xen/include/acpi/cpufreq/cpufreq.h
@@ -225,8 +225,8 @@ struct cpu_dbs_info_s {
struct cpufreq_frequency_table *freq_table;
int cpu;
unsigned int enable:1;
- unsigned int stoppable:1;
unsigned int turbo_enabled:1;
+ int8_t stoppable;
};
int cpufreq_governor_dbs(struct cpufreq_policy *policy, unsigned int event);
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