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Subject: Re: [PATCH 1/2] coresight: trbe: Fix TRBE potential sleep in atomic
 context
To:     Suzuki K Poulose <suzuki.poulose@arm.com>,
        Junhao He <hejunhao3@huawei.com>, <mike.leach@linaro.org>,
        <leo.yan@linaro.org>, <anshuman.khandual@arm.com>,
        <jonathan.cameron@huawei.com>
References: <20230814093813.19152-1-hejunhao3@huawei.com>
 <20230814093813.19152-2-hejunhao3@huawei.com>
 <37e36bde-fc70-6d2d-8dec-28e572f618cc@arm.com>
CC:     <coresight@lists.linaro.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>, <yangyicong@huawei.com>,
        <prime.zeng@hisilicon.com>
From:   hejunhao <hejunhao3@huawei.com>
Message-ID: <4049aee1-7f4d-5a54-ce27-7d802ae9616d@huawei.com>
Date:   Mon, 14 Aug 2023 21:32:29 +0800
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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 ?

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);
>> +    }
>>       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;
>>   }
>
>
> .
>