| Message ID | 1470244135-979-1-git-send-email-sudeep.holla@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi, Sebastian, as a heads-up, the issue below issue may apply to over hotplug state machine conversions if a mutex was added. On Wed, Aug 03, 2016 at 06:08:55PM +0100, Sudeep Holla wrote: > 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> I haven't been able to come up with a race with hotplug that halted forward progress, and otherwise this is at least as structurally correct as the mutex, so FWIW: Acked-by: Mark Rutland <mark.rutland@arm.com> Mark. > --- > 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 >
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); }
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(-) -- 2.7.4