If the stop machinery is called from inactive CPU we cannot use
lg_global_lock(), because some other stomp machine invocation might be
in progress and the lock can be contended. We cannot schedule from this
context, so use the lovely new lg_global_trylock_relax() primitive to
do what we used to do via one mutex_trylock()/cpu_relax() loop. We
now do that trylock()/relax() across an entire herd of locks. Joy.
Signed-off-by: Mike Galbraith <umgwanakikbuti@xxxxxxxxx>
---
kernel/stop_machine.c | 24 ++++++++++++++----------
1 file changed, 14 insertions(+), 10 deletions(-)
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -266,7 +266,7 @@ int stop_two_cpus(unsigned int cpu1, uns
struct irq_cpu_stop_queue_work_info call_args;
struct multi_stop_data msdata;
- preempt_disable();
+ preempt_disable_nort();
msdata = (struct multi_stop_data){
.fn = fn,
.data = arg,
@@ -299,7 +299,7 @@ int stop_two_cpus(unsigned int cpu1, uns
* This relies on the stopper workqueues to be FIFO.
*/
if (!cpu_active(cpu1) || !cpu_active(cpu2)) {
- preempt_enable();
+ preempt_enable_nort();
return -ENOENT;
}
@@ -313,7 +313,7 @@ int stop_two_cpus(unsigned int cpu1, uns
&irq_cpu_stop_queue_work,
&call_args, 1);
lg_local_unlock(&stop_cpus_lock);
- preempt_enable();
+ preempt_enable_nort();
wait_for_stop_done(&done);
@@ -346,7 +346,7 @@ static DEFINE_PER_CPU(struct cpu_stop_wo
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;
@@ -360,11 +360,13 @@ static void queue_stop_cpus_work(const s
}
/*
- * Disable preemption while queueing to avoid getting
- * preempted by a stopper which might wait for other stoppers
- * to enter @fn which can lead to deadlock.
+ * Make sure that all work is queued on all cpus before
+ * any of the cpus can execute it.
*/
- lg_global_lock(&stop_cpus_lock);
+ if (!inactive)
+ lg_global_lock(&stop_cpus_lock);
+ else
+ lg_global_trylock_relax(&stop_cpus_lock);
for_each_cpu(cpu, cpumask)
cpu_stop_queue_work(cpu, &per_cpu(stop_cpus_work, cpu));
lg_global_unlock(&stop_cpus_lock);
@@ -376,7 +378,7 @@ static int __stop_cpus(const struct cpum
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;
}
@@ -572,6 +574,8 @@ static int __init cpu_stop_init(void)
INIT_LIST_HEAD(&stopper->works);
}
+ lg_lock_init(&stop_cpus_lock, "stop_cpus_lock");
+
BUG_ON(smpboot_register_percpu_thread(&cpu_stop_threads));
stop_machine_initialized = true;
return 0;
@@ -667,7 +671,7 @@ int stop_machine_from_inactive_cpu(int (
set_state(&msdata, MULTI_STOP_PREPARE);
cpu_stop_init_done(&done, num_active_cpus());
queue_stop_cpus_work(cpu_active_mask, multi_cpu_stop, &msdata,
- &done);
+ &done, true);
ret = multi_cpu_stop(&msdata);
/* Busy wait for completion. */
--
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