Re: [PATCH V8 1/4] perf/core: Add PERF_SAMPLE_DATA_PAGE_SIZE

[Liang, Kan]

On 9/30/2020 3:15 AM, Stephane Eranian wrote:
> > +static u64 perf_get_page_size(unsigned long addr)
> > +{
> > +       unsigned long flags;
> > +       u64 size;
> > +
> > +       if (!addr)
> > +               return 0;
> > +
> > +       /*
> > +        * Software page-table walkers must disable IRQs,
> > +        * which prevents any tear down of the page tables.
> > +        */
> > +       local_irq_save(flags);
> > +
> > +       size = __perf_get_page_size(current->active_mm, addr);
> > +
> When I tested on my kernel, it panicked because I suspect
> current->active_mm could be NULL. Adding a check for NULL avoided the
> problem. But I suspect this is not the correct solution.

I guess the NULL active_mm should be a rare case. If so, I think it's 
not bad to add a check and return 0 page size.


Thanks,
Kan