Re: [PATCH 1/2] coresight: trbe: Fix TRBE potential sleep in atomic context

[hejunhao <hejunhao3@huawei.com>]

Hi Suzuki


On 2023/8/15 6:57, Suzuki K Poulose wrote:
> On 14/08/2023 14:32, hejunhao wrote:
>> Hi Suzuki
>>
>>
>> On 2023/8/14 18:34, Suzuki K Poulose wrote:
>>> Hi Junhao
>>>
>>> On 14/08/2023 10:38, Junhao He wrote:
>>>> smp_call_function_single() will allocate an IPI interrupt vector to
>>>> the target processor and send a function call request to the interrupt
>>>> vector. After the target processor receives the IPI interrupt, it will
>>>> execute arm_trbe_remove_coresight_cpu() call request in the interrupt
>>>> handler.
>>>>
>>>> According to the device_unregister() stack information, if other 
>>>> process
>>>> is useing the device, the down_write() may sleep, and trigger 
>>>> deadlocks
>>>> or unexpected errors.
>>>>
>>>>    arm_trbe_remove_coresight_cpu
>>>>      coresight_unregister
>>>>        device_unregister
>>>>          device_del
>>>>            kobject_del
>>>>              __kobject_del
>>>>                sysfs_remove_dir
>>>>                  kernfs_remove
>>>>                    down_write ---------> it may sleep
>>>>
>>>> Add a helper arm_trbe_disable_cpu() to disable TRBE precpu irq and 
>>>> reset
>>>> per TRBE.
>>>> Simply call arm_trbe_remove_coresight_cpu() directly without useing 
>>>> the
>>>> smp_call_function_single(), which is the same as registering the TRBE
>>>> coresight device.
>>>>
>>>> Fixes: 3fbf7f011f24 ("coresight: sink: Add TRBE driver")
>>>> Signed-off-by: Junhao He <hejunhao3@huawei.com>
>>>> ---
>>>>   drivers/hwtracing/coresight/coresight-trbe.c | 35 
>>>> +++++++++++---------
>>>>   1 file changed, 20 insertions(+), 15 deletions(-)
>>>>
>>>> diff --git a/drivers/hwtracing/coresight/coresight-trbe.c 
>>>> b/drivers/hwtracing/coresight/coresight-trbe.c
>>>> index 7720619909d6..ce1e6f537b8d 100644
>>>> --- a/drivers/hwtracing/coresight/coresight-trbe.c
>>>> +++ b/drivers/hwtracing/coresight/coresight-trbe.c
>>>> @@ -1225,6 +1225,17 @@ static void arm_trbe_enable_cpu(void *info)
>>>>       enable_percpu_irq(drvdata->irq, IRQ_TYPE_NONE);
>>>>   }
>>>>   +static void arm_trbe_disable_cpu(void *info)
>>>> +{
>>>> +    struct trbe_drvdata *drvdata = info;
>>>> +    struct trbe_cpudata *cpudata = this_cpu_ptr(drvdata->cpudata);
>>>> +
>>>> +    disable_percpu_irq(drvdata->irq);
>>>> +    trbe_reset_local(cpudata);
>>>> +    cpudata->drvdata = NULL;
>>>> +}
>>>> +
>>>> +
>>>>   static void arm_trbe_register_coresight_cpu(struct trbe_drvdata 
>>>> *drvdata, int cpu)
>>>>   {
>>>>       struct trbe_cpudata *cpudata = per_cpu_ptr(drvdata->cpudata, 
>>>> cpu);
>>>> @@ -1326,18 +1337,12 @@ static void arm_trbe_probe_cpu(void *info)
>>>>       cpumask_clear_cpu(cpu, &drvdata->supported_cpus);
>>>>   }
>>>>   -static void arm_trbe_remove_coresight_cpu(void *info)
>>>> +static void arm_trbe_remove_coresight_cpu(struct trbe_drvdata 
>>>> *drvdata, int cpu)
>>>>   {
>>>> -    int cpu = smp_processor_id();
>>>> -    struct trbe_drvdata *drvdata = info;
>>>> -    struct trbe_cpudata *cpudata = per_cpu_ptr(drvdata->cpudata, 
>>>> cpu);
>>>>       struct coresight_device *trbe_csdev = 
>>>> coresight_get_percpu_sink(cpu);
>>>>   -    disable_percpu_irq(drvdata->irq);
>>>> -    trbe_reset_local(cpudata);
>>>>       if (trbe_csdev) {
>>>>           coresight_unregister(trbe_csdev);
>>>> -        cpudata->drvdata = NULL;
>>>>           coresight_set_percpu_sink(cpu, NULL);
>>>
>>> I am a bit concerned about "resetting" the sink from a different CPU.
>>> Could we instead, schedule a delayed work to unregister the trbe_csdev?
>>
>> Yes, I will try to do that.
>> Sorry for my following questions.
>> As you mean, do we need to take the same care when setting the percpu 
>> sink
>> in the register trbe_csdev ?
>
> Apologies, having taken another look, we set the percpu_sink for
> a cpu outside smp_call_function(). So, I think your patch is fine.
>
>
>>
>> Best regards,
>> Junhao.
>>
>>>
>>>
>>>>       }
>>>>   }
>>>> @@ -1366,8 +1371,12 @@ static int arm_trbe_remove_coresight(struct 
>>>> trbe_drvdata *drvdata)
>>>>   {
>>>>       int cpu;
>>>>   -    for_each_cpu(cpu, &drvdata->supported_cpus)
>>>> -        smp_call_function_single(cpu, 
>>>> arm_trbe_remove_coresight_cpu, drvdata, 1);
>>>> +    for_each_cpu(cpu, &drvdata->supported_cpus) {
>>>> +        if (cpumask_test_cpu(cpu, &drvdata->supported_cpus))
>>>> +            smp_call_function_single(cpu, arm_trbe_disable_cpu, 
>>>> drvdata, 1);
>>>> +        if (cpumask_test_cpu(cpu, &drvdata->supported_cpus))
>>>> +            arm_trbe_remove_coresight_cpu(drvdata, cpu);
>
> Do we need to test the cpu here in both places ? We already check that
> in the loop entry. The reason why we repeat the check during the probe,
> is to skip any CPUs that may have a TRBE not accessible.
>
> Suzuki
>

Ok, Will fix in next version.

Best regards,
Junhao.

>
>>>> +    }
>>>>       free_percpu(drvdata->cpudata);
>>>>       return 0;
>>>>   }
>>>> @@ -1406,12 +1415,8 @@ static int arm_trbe_cpu_teardown(unsigned 
>>>> int cpu, struct hlist_node *node)
>>>>   {
>>>>       struct trbe_drvdata *drvdata = hlist_entry_safe(node, struct 
>>>> trbe_drvdata, hotplug_node);
>>>>   -    if (cpumask_test_cpu(cpu, &drvdata->supported_cpus)) {
>>>> -        struct trbe_cpudata *cpudata = 
>>>> per_cpu_ptr(drvdata->cpudata, cpu);
>>>> -
>>>> -        disable_percpu_irq(drvdata->irq);
>>>> -        trbe_reset_local(cpudata);
>>>> -    }
>>>> +    if (cpumask_test_cpu(cpu, &drvdata->supported_cpus))
>>>> +        arm_trbe_disable_cpu(drvdata);
>>>>       return 0;
>>>>   }
>>>
>>>
>>> .
>>>
>>
>
>
> .
>


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