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

[Stephane Eranian]

On Wed, Sep 30, 2020 at 7:48 AM Dave Hansen <dave.hansen@xxxxxxxxx> wrote:
>
> On 9/30/20 7:42 AM, Liang, Kan wrote:
> >> 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.
>
> I think it would be best to understand why ->active_mm is NULL instead
> of just papering over the problem.  If it is papered over, and this is
> common, you might end up effectively turning off your shiny new feature
> inadvertently.

I tried that on a backport of the patch to an older kernel. Maybe the
behavior of active_mm has change compared to tip.git.
I will try again with tip.git.