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

[Suzuki K Poulose]

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@xxxxxxxxxx>
> > > ---
> > >   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


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