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Date: Wed, 28 Jun 2017 21:41:23 +0200 (CEST)
From: Thomas Gleixner <tglx@...utronix.de>
To: Anju T Sudhakar <anju@...ux.vnet.ibm.com>
cc: mpe@...erman.id.au, linux-kernel@...r.kernel.org,
linuxppc-dev@...ts.ozlabs.org, ego@...ux.vnet.ibm.com,
bsingharora@...il.com, anton@...ba.org, sukadev@...ux.vnet.ibm.com,
mikey@...ling.org, stewart@...ux.vnet.ibm.com, dja@...ens.net,
eranian@...gle.com, hemant@...ux.vnet.ibm.com,
maddy@...ux.vnet.ibm.com
Subject: Re: [PATCH v11 07/10] powerpc/perf: PMU functions for Core IMC and
hotplugging
On Thu, 29 Jun 2017, Anju T Sudhakar wrote:
> +static void cleanup_all_core_imc_memory(struct imc_pmu *pmu_ptr)
> +{
> + struct imc_mem_info *ptr;
> +
> + for (ptr = pmu_ptr->mem_info; ptr; ptr++) {
> + if (ptr->vbase[0])
> + free_pages((u64)ptr->vbase[0], 0);
> + }
This loop is broken beyond repair. If pmu_ptr->mem_info is not NULL, then
ptr will happily increment to the point where it wraps around to
NULL. Oh well.
> + kfree(pmu_ptr->mem_info);
> +bool is_core_imc_mem_inited(int cpu)
This function is global because?
> +{
> + struct imc_mem_info *mem_info;
> + int core_id = (cpu / threads_per_core);
> +
> + mem_info = &core_imc_pmu->mem_info[core_id];
> + if ((mem_info->id == core_id) && (mem_info->vbase[0] != NULL))
> + return true;
> +
> + return false;
> +}
> +
> +/*
> + * imc_mem_init : Function to support memory allocation for core imc.
> + */
> +static int imc_mem_init(struct imc_pmu *pmu_ptr)
> +{
The function placement is horrible. This function belongs to the pmu init
stuff and wants to be placed there and not five pages away in the middle of
unrelated functions.
> + int nr_cores;
> +
> + if (pmu_ptr->imc_counter_mmaped)
> + return 0;
> + nr_cores = num_present_cpus() / threads_per_core;
> + pmu_ptr->mem_info = kzalloc((sizeof(struct imc_mem_info) * nr_cores), GFP_KERNEL);
> + if (!pmu_ptr->mem_info)
> + return -ENOMEM;
> + return 0;
> +}
> +static int core_imc_event_init(struct perf_event *event)
> +{
> + int core_id, rc;
> + u64 config = event->attr.config;
> + struct imc_mem_info *pcmi;
> + struct imc_pmu *pmu;
> +
> + if (event->attr.type != event->pmu->type)
> + return -ENOENT;
> +
> + /* Sampling not supported */
> + if (event->hw.sample_period)
> + return -EINVAL;
> +
> + /* unsupported modes and filters */
> + if (event->attr.exclude_user ||
> + event->attr.exclude_kernel ||
> + event->attr.exclude_hv ||
> + event->attr.exclude_idle ||
> + event->attr.exclude_host ||
> + event->attr.exclude_guest)
> + return -EINVAL;
> +
> + if (event->cpu < 0)
> + return -EINVAL;
> +
> + event->hw.idx = -1;
> + pmu = imc_event_to_pmu(event);
> +
> + /* Sanity check for config (event offset and rvalue) */
> + if (((config & IMC_EVENT_OFFSET_MASK) > pmu->counter_mem_size) ||
> + ((config & IMC_EVENT_RVALUE_MASK) != 0))
> + return -EINVAL;
> +
> + if (!is_core_imc_mem_inited(event->cpu))
> + return -ENODEV;
> +
> + core_id = event->cpu / threads_per_core;
> + pcmi = &pmu->mem_info[core_id];
> + if ((pcmi->id != core_id) || (!pcmi->vbase[0]))
> + return -ENODEV;
> +
> + event->hw.event_base = (u64)pcmi->vbase[0] + (config & IMC_EVENT_OFFSET_MASK);
> + /*
> + * Core pmu units are enabled only when it is used.
> + * See if this is triggered for the first time.
> + * If yes, take the mutex lock and enable the core counters.
> + * If not, just increment the count in core_events.
> + */
> + if (atomic_inc_return(&core_events[core_id]) == 1) {
> + mutex_lock(&imc_core_reserve);
> + rc = opal_imc_counters_start(OPAL_IMC_COUNTERS_CORE,
> + get_hard_smp_processor_id(event->cpu));
> + mutex_unlock(&imc_core_reserve);
That machinery here is racy as hell in several aspects.
CPU0 CPU1
atomic_inc_ret(core_events[0]) -> 1
preemption()
atomic_inc_ret(core_events[0]) -> 2
return 0;
Uses the event, without counters
being started until the preempted
task comes on the CPU again.
Here is another one:
CPU0 CPU1
atomic_dec_ret(core_events[0]) -> 0
atomic_inc_ret(core_events[1] -> 1
mutex_lock();
mutex_lock() start counter();
mutex_unlock()
stop_counter();
mutex_unlock();
Yay, another stale event!
Brilliant stuff that, or maybe not so much.
> + if (rc) {
> + atomic_dec_return(&core_events[core_id]);
What's the point of using atomic_dec_return here if you ignore the return
value? Not that it matters much as the whole logic is crap anyway.
> + pr_err("IMC: Unable to start the counters for core %d\n", core_id);
> + return -ENODEV;
> + }
> + }
> @@ -410,22 +658,38 @@ int init_imc_pmu(struct imc_events *events, int idx,
> struct imc_pmu *pmu_ptr)
> {
> int ret = -ENODEV;
> +
Sure ret needs to stay initialized, just in case imc_mem_init() does not
return anything magically, right?
> + ret = imc_mem_init(pmu_ptr);
> + if (ret)
> + goto err_free;
> /* Add cpumask and register for hotplug notification */
> - if (atomic_inc_return(&nest_pmus) == 1) {
> - /*
> - * Nest imc pmu need only one cpu per chip, we initialize the
> - * cpumask for the first nest imc pmu and use the same for the rest.
> - * To handle the cpuhotplug callback unregister, we track
> - * the number of nest pmus registers in "nest_pmus".
> - * "nest_imc_cpumask_initialized" is set to zero during cpuhotplug
> - * callback unregister.
> - */
> - ret = nest_pmu_cpumask_init();
> + switch (pmu_ptr->domain) {
> + case IMC_DOMAIN_NEST:
> + if (atomic_inc_return(&nest_pmus) == 1) {
> + /*
> + * Nest imc pmu need only one cpu per chip, we initialize
> + * the cpumask for the first nest imc pmu and use the
> + * same for the rest.
> + * To handle the cpuhotplug callback unregister, we track
> + * the number of nest pmus registers in "nest_pmus".
> + * "nest_imc_cpumask_initialized" is set to zero during
> + * cpuhotplug callback unregister.
> + */
> + ret = nest_pmu_cpumask_init();
> + if (ret)
> + goto err_free;
> + mutex_lock(&imc_nest_inited_reserve);
> + nest_imc_cpumask_initialized = 1;
> + mutex_unlock(&imc_nest_inited_reserve);
> + }
> + break;
> + case IMC_DOMAIN_CORE:
> + ret = core_imc_pmu_cpumask_init();
> if (ret)
> - goto err_free;
> - mutex_lock(&imc_nest_inited_reserve);
> - nest_imc_cpumask_initialized = 1;
> - mutex_unlock(&imc_nest_inited_reserve);
> + return ret;
Oh, so now you replaced the goto with ret. What is actually taking care of
the cleanup if that fails?
> + break;
> + default:
> + return -1; /* Unknown domain */
> }
> ret = update_events_in_group(events, idx, pmu_ptr);
> if (ret)
> @@ -459,5 +723,10 @@ int init_imc_pmu(struct imc_events *events, int idx,
> mutex_unlock(&imc_nest_inited_reserve);
> }
> }
> + /* For core_imc, we have allocated memory, we need to free it */
> + if (pmu_ptr->domain == IMC_DOMAIN_CORE) {
> + cleanup_all_core_imc_memory(pmu_ptr);
> + cpuhp_remove_state(CPUHP_AP_PERF_POWERPC_CORE_IMC_ONLINE);
Cute. You cleanuo the memory stuff and then you let the hotplug core invoke
the offline callbacks which then deal with freed memory.
Thanks,
tglx
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