[PATCH RT 7/8] stomp_machine: Use mutex_trylock when called from inactive cpu

Steven Rostedt
2012-10-12T01:21:40Z

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From: Thomas Gleixner <tglx@linutronix.de>

If the stop machinery is called from inactive CPU we cannot use
mutex_lock, because some other stomp machine invokation might be in
progress and the mutex can be contended. We cannot schedule from this
context, so trylock and loop.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable-rt@vger.kernel.org
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
kernel/stop_machine.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index 561ba3a..e98c70b 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -158,7 +158,7 @@ static DEFINE_PER_CPU(struct cpu_stop_work, stop_cpus_work);

static void queue_stop_cpus_work(const struct cpumask *cpumask,
cpu_stop_fn_t fn, void *arg,
- struct cpu_stop_done *done)
+ struct cpu_stop_done *done, bool inactive)
{
struct cpu_stop_work *work;
unsigned int cpu;
@@ -175,7 +175,12 @@ static void queue_stop_cpus_work(const struct cpumask *cpumask,
* Make sure that all work is queued on all cpus before we
* any of the cpus can execute it.
*/
- mutex_lock(&stopper_lock);
+ if (!inactive) {
+ mutex_lock(&stopper_lock);
+ } else {
+ while (!mutex_trylock(&stopper_lock))
+ cpu_relax();
+ }
for_each_cpu(cpu, cpumask)
cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu),
&per_cpu(stop_cpus_work, cpu));
@@ -188,7 +193,7 @@ static int __stop_cpus(const struct cpumask *cpumask,
struct cpu_stop_done done;

cpu_stop_init_done(&done, cpumask_weight(cpumask));
- queue_stop_cpus_work(cpumask, fn, arg, &done);
+ queue_stop_cpus_work(cpumask, fn, arg, &done, false);
wait_for_stop_done(&done);
return done.executed ? done.ret : -ENOENT;
}
@@ -601,7 +606,7 @@ int stop_machine_from_inactive_cpu(int (*fn)(void *), void *data,
set_state(&smdata, STOPMACHINE_PREPARE);
cpu_stop_init_done(&done, num_active_cpus());
queue_stop_cpus_work(cpu_active_mask, stop_machine_cpu_stop, &smdata,
- &done);
+ &done, true);
ret = stop_machine_cpu_stop(&smdata);

/* Busy wait for completion. */
--
1.7.10.4