Re: [PATCH v2 1/2] coresight: trbe: Fix TRBE potential sleep in atomic context

[hejunhao <hejunhao3@huawei.com>]

Hi Anshuman Khandual,


On 2023/8/17 15:13, Anshuman Khandual wrote:
> Hello Junhao,
>
> On 8/16/23 19:40, Suzuki K Poulose wrote:
>> From: Junhao He <hejunhao3@huawei.com>
>>
>> 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
> But how did you really detect this problem ? Does this show up as an warning when
> you enable lockdep debug ? OR it really happened during a real workload execution
> followed by TRBE module unload. Although the problem seems plausible (which needs
> fixing), just wondering how did we trigger this.

Yes, it really happened during a real workload.

If the TRBE driver is loaded and unloaded cyclically. the test script 
following:

   for ((i=0;i<99999;i++))
   do
   insmod coresight-trbe.ko;
   rmmod coresight-trbe.ko;
   echo "loop $i";
   done

The kernel will report a panic.

>> 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>
>> Link: https://lore.kernel.org/r/20230814093813.19152-2-hejunhao3@huawei.com
>> [ Remove duplicate cpumask checks during removal ]
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
>> ---
>>   drivers/hwtracing/coresight/coresight-trbe.c | 33 +++++++++++---------
>>   1 file changed, 18 insertions(+), 15 deletions(-)
>>
>> diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c
>> index 7720619909d6..025f70adee47 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);
>>   	}
>>   }
>> @@ -1366,8 +1371,10 @@ 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) {
>> +		smp_call_function_single(cpu, arm_trbe_disable_cpu, drvdata, 1);
>> +		arm_trbe_remove_coresight_cpu(drvdata, cpu);
>> +	}
>>   	free_percpu(drvdata->cpudata);
>>   	return 0;
>>   }
>> @@ -1406,12 +1413,8 @@ 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);
> This code hunk seems unrelated to the context here other than just finding another use case
> for arm_trbe_disable_cpu(). The problem is - arm_trbe_disable_cpu() resets cpudata->drvdata
> which might not get re-initialized back in arm_trbe_cpu_startup(), as there will still be a
> per cpu sink associated as confirmed with coresight_get_percpu_sink(). I guess it might be
> better to drop this change and just keep everything limited to SMP IPI callback reworking in
> arm_trbe_remove_coresight().

OK, will fix it. The change is just to simplify the code of cpu_teardown.
Maybe we can consider whether we need to set "cpudata->drvdata = NULL"
in arm_trbe_disable_cpu()?  If it's not necessary, This can be kept.
Then drop the release cpudata->drvdata from arm_trbe_disable_cpu().

Best regards,
Junhao.

>>   	return 0;
>>   }
>>   
> .
>