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

[Suzuki K Poulose]

On 17/08/2023 08:13, 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.

I was able to trigger this with just :

modprobe coresight-trbe; modprobe -r coresight-trbe;

With all the bells and whistles enabled in the kernel.

Suzuki