Re: [PATCH v5 2/4] cacheinfo: Allocate memory for memory if not done from the primary CPU

[Sudeep Holla <sudeep.holla@arm.com>]

On Wed, Aug 28, 2024 at 04:16:00PM +0300, Nikolay Borisov wrote:
> 
> On 27.08.24 г. 8:16 ч., Ricardo Neri wrote:
> > Commit 5944ce092b97 ("arch_topology: Build cacheinfo from primary CPU")
> > adds functionality that architectures can use to optionally allocate and
> > build cacheinfo early during boot. Commit 6539cffa9495 ("cacheinfo: Add
> > arch specific early level initializer") lets secondary CPUs correct (and
> > reallocate memory) cacheinfo data if needed.
> > 
> > If the early build functionality is not used and cacheinfo does not need
> > correction, memory for cacheinfo is never allocated. x86 does not use the
> > early build functionality. Consequently, during the cacheinfo CPU hotplug
> > callback, last_level_cache_is_valid() attempts to dereference a NULL
> > pointer:
> > 
> >       BUG: kernel NULL pointer dereference, address: 0000000000000100
> >       #PF: supervisor read access in kernel mode
> >       #PF: error_code(0x0000) - not present page
> >       PGD 0 P4D 0
> >       Oops: 0000 [#1] PREEPMT SMP NOPTI
> >       CPU: 0 PID 19 Comm: cpuhp/0 Not tainted 6.4.0-rc2 #1
> >       RIP: 0010: last_level_cache_is_valid+0x95/0xe0a
> > 
> > Allocate memory for cacheinfo during the cacheinfo CPU hotplug callback if
> > not done earlier.
> 
> I assume instead of duplicating "memory" in the subject you meant
> "cacheinfo" ?
>

Good point, +1 for the $subject change. I clearly missed to notice that.

-- 
Regards,
Sudeep