[PATCH] drivers/perf: arm-pmu: convert arm_pmu_mutex to spinlock

Sudeep Holla
2016-08-03T17:08:55Z

arm_pmu_mutex is never held long and we don't want to sleep while the
lock is being held as it's executed in the context of hotplug notifiers.
So it can be converted to a simple spinlock instead.

Without this patch we get the following warning:

BUG: sleeping function called from invalid context at kernel/locking/mutex.c:620
in_atomic(): 1, irqs_disabled(): 128, pid: 0, name: swapper/2
no locks held by swapper/2/0.
irq event stamp: 381314
hardirqs last enabled at (381313): _raw_spin_unlock_irqrestore+0x7c/0x88
hardirqs last disabled at (381314): cpu_die+0x28/0x48
softirqs last enabled at (381294): _local_bh_enable+0x28/0x50
softirqs last disabled at (381293): irq_enter+0x58/0x78
CPU: 2 PID: 0 Comm: swapper/2 Not tainted 4.7.0 #12
Call trace:
dump_backtrace+0x0/0x220
show_stack+0x24/0x30
dump_stack+0xb4/0xf0
___might_sleep+0x1d8/0x1f0
__might_sleep+0x5c/0x98
mutex_lock_nested+0x54/0x400
arm_perf_starting_cpu+0x34/0xb0
cpuhp_invoke_callback+0x88/0x3d8
notify_cpu_starting+0x78/0x98
secondary_start_kernel+0x108/0x1a8

This patch converts the mutex to spinlock to eliminate the above
warnings. This constraints pmu->reset to be non-blocking call which is
the case with all the ARM PMU backends.

Fixes: 37b502f121ad ("arm/perf: Fix hotplug state machine conversion")
Cc: Stephen Boyd <sboyd@codeaurora.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
---
drivers/perf/arm_pmu.c | 18 +++++++++---------
1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
index 6ccb994bdfcb..4c9a537a1265 100644
--- a/drivers/perf/arm_pmu.c
+++ b/drivers/perf/arm_pmu.c
@@ -688,7 +688,7 @@ static int cpu_pmu_request_irq(struct arm_pmu *cpu_pmu, irq_handler_t handler)
return 0;
}

-static DEFINE_MUTEX(arm_pmu_mutex);
+static DEFINE_SPINLOCK(arm_pmu_lock);
static LIST_HEAD(arm_pmu_list);

/*
@@ -701,7 +701,7 @@ static int arm_perf_starting_cpu(unsigned int cpu)
{
struct arm_pmu *pmu;

- mutex_lock(&arm_pmu_mutex);
+ spin_lock(&arm_pmu_lock);
list_for_each_entry(pmu, &arm_pmu_list, entry) {

if (!cpumask_test_cpu(cpu, &pmu->supported_cpus))
@@ -709,7 +709,7 @@ static int arm_perf_starting_cpu(unsigned int cpu)
if (pmu->reset)
pmu->reset(pmu);
}
- mutex_unlock(&arm_pmu_mutex);
+ spin_unlock(&arm_pmu_lock);
return 0;
}

@@ -821,9 +821,9 @@ static int cpu_pmu_init(struct arm_pmu *cpu_pmu)
if (!cpu_hw_events)
return -ENOMEM;

- mutex_lock(&arm_pmu_mutex);
+ spin_lock(&arm_pmu_lock);
list_add_tail(&cpu_pmu->entry, &arm_pmu_list);
- mutex_unlock(&arm_pmu_mutex);
+ spin_unlock(&arm_pmu_lock);

err = cpu_pm_pmu_register(cpu_pmu);
if (err)
@@ -859,9 +859,9 @@ static int cpu_pmu_init(struct arm_pmu *cpu_pmu)
return 0;

out_unregister:
- mutex_lock(&arm_pmu_mutex);
+ spin_lock(&arm_pmu_lock);
list_del(&cpu_pmu->entry);
- mutex_unlock(&arm_pmu_mutex);
+ spin_unlock(&arm_pmu_lock);
free_percpu(cpu_hw_events);
return err;
}
@@ -869,9 +869,9 @@ static int cpu_pmu_init(struct arm_pmu *cpu_pmu)
static void cpu_pmu_destroy(struct arm_pmu *cpu_pmu)
{
cpu_pm_pmu_unregister(cpu_pmu);
- mutex_lock(&arm_pmu_mutex);
+ spin_lock(&arm_pmu_lock);
list_del(&cpu_pmu->entry);
- mutex_unlock(&arm_pmu_mutex);
+ spin_unlock(&arm_pmu_lock);
free_percpu(cpu_pmu->hw_events);
}

--
2.7.4