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

[James Clark]

On 17/08/2023 09:41, hejunhao wrote:
> 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@xxxxxxxxxx>
>>>
>>> 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.
> 

I wonder how easy it would be to add a kselftest to do this with all of
the Coresight modules. Because we also had a problem with bad reference
counting preventing an unload of the CTI module. Although that did
require starting a perf session, which might complicated the test.

>>> 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@xxxxxxxxxx>
>>> Link:
>>> https://lore.kernel.org/r/20230814093813.19152-2-hejunhao3@xxxxxxxxxx
>>> [ Remove duplicate cpumask checks during removal ]
>>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
>>> ---
>>>   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;
>>>   }
>>>   
>> .
>>
> 
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