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SubjectRe: [PATCH 1/2] coresight: trbe: Fix TRBE potential sleep in atomic context
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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;
>> }
>
>
> .
>

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