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Subject[RFC PATCH 4/6] stop_machine: kill stop_cpus_mutex
Change the users of stop_cpus_mutex to rely on stop_work_alloc() and
stop_work_free(). This means that 2 stop_cpus() can run in parallel
as long a their cpumask's do not overlap.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
kernel/stop_machine.c | 16 ++++++----------
1 files changed, 6 insertions(+), 10 deletions(-)

diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index 3d5d810..4b23875 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -343,9 +343,6 @@ void stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
cpu_stop_queue_work(cpu, work_buf);
}

-/* static data for stop_cpus */
-static DEFINE_MUTEX(stop_cpus_mutex);
-
static void queue_stop_cpus_work(const struct cpumask *cpumask,
cpu_stop_fn_t fn, void *arg,
struct cpu_stop_done *done)
@@ -412,10 +409,9 @@ int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
{
int ret;

- /* static works are used, process one request at a time */
- mutex_lock(&stop_cpus_mutex);
+ stop_work_alloc(cpumask, true);
ret = __stop_cpus(cpumask, fn, arg);
- mutex_unlock(&stop_cpus_mutex);
+ stop_work_free(cpumask);
return ret;
}

@@ -442,10 +438,10 @@ int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
int ret;

/* static works are used, process one request at a time */
- if (!mutex_trylock(&stop_cpus_mutex))
+ if (!stop_work_alloc(cpumask, false))
return -EAGAIN;
ret = __stop_cpus(cpumask, fn, arg);
- mutex_unlock(&stop_cpus_mutex);
+ stop_work_free(cpumask);
return ret;
}

@@ -643,7 +639,7 @@ int stop_machine_from_inactive_cpu(int (*fn)(void *), void *data,
msdata.num_threads = num_active_cpus() + 1; /* +1 for local */

/* No proper task established and can't sleep - busy wait for lock. */
- while (!mutex_trylock(&stop_cpus_mutex))
+ while (!stop_work_alloc(cpus, false))
cpu_relax();

/* Schedule work on other CPUs and execute directly for local CPU */
@@ -656,8 +652,8 @@ int stop_machine_from_inactive_cpu(int (*fn)(void *), void *data,
/* Busy wait for completion. */
while (!completion_done(&done.completion))
cpu_relax();
+ stop_work_free(cpus);

- mutex_unlock(&stop_cpus_mutex);
return ret ?: done.ret;
}

--
1.5.5.1


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