Re: [PATCH v8 04/16] ACPI: processor: Move checks and availability of acpi_processor earlier

["Rafael J. Wysocki" <rafael@kernel.org>]

On Tue, Apr 30, 2024 at 12:45 PM Jonathan Cameron
<Jonathan.Cameron@huawei.com> wrote:
>
> On Tue, 30 Apr 2024 12:17:38 +0200
> "Rafael J. Wysocki" <rafael@kernel.org> wrote:
>
> > On Tue, Apr 30, 2024 at 12:13 PM Jonathan Cameron
> > <Jonathan.Cameron@huawei.com> wrote:
> > >
> > > On Tue, 30 Apr 2024 10:28:38 +0100
> > > Jonathan Cameron <Jonathan.Cameron@Huawei.com> wrote:
> > >
> > > > On Tue, 30 Apr 2024 14:17:24 +1000
> > > > Gavin Shan <gshan@redhat.com> wrote:
> > > >
> > > > > On 4/26/24 23:51, Jonathan Cameron wrote:
> > > > > > Make the per_cpu(processors, cpu) entries available earlier so that
> > > > > > they are available in arch_register_cpu() as ARM64 will need access
> > > > > > to the acpi_handle to distinguish between acpi_processor_add()
> > > > > > and earlier registration attempts (which will fail as _STA cannot
> > > > > > be checked).
> > > > > >
> > > > > > Reorder the remove flow to clear this per_cpu() after
> > > > > > arch_unregister_cpu() has completed, allowing it to be used in
> > > > > > there as well.
> > > > > >
> > > > > > Note that on x86 for the CPU hotplug case, the pr->id prior to
> > > > > > acpi_map_cpu() may be invalid. Thus the per_cpu() structures
> > > > > > must be initialized after that call or after checking the ID
> > > > > > is valid (not hotplug path).
> > > > > >
> > > > > > Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > > > > >
> > > > > > ---
> > > > > > v8: On buggy bios detection when setting per_cpu structures
> > > > > >      do not carry on.
> > > > > >      Fix up the clearing of per cpu structures to remove unwanted
> > > > > >      side effects and ensure an error code isn't use to reference them.
> > > > > > ---
> > > > > >   drivers/acpi/acpi_processor.c | 79 +++++++++++++++++++++--------------
> > > > > >   1 file changed, 48 insertions(+), 31 deletions(-)
> > > > > >
> > > > > > diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
> > > > > > index ba0a6f0ac841..3b180e21f325 100644
> > > > > > --- a/drivers/acpi/acpi_processor.c
> > > > > > +++ b/drivers/acpi/acpi_processor.c
> > > > > > @@ -183,8 +183,38 @@ static void __init acpi_pcc_cpufreq_init(void) {}
> > > > > >   #endif /* CONFIG_X86 */
> > > > > >
> > > > > >   /* Initialization */
> > > > > > +static DEFINE_PER_CPU(void *, processor_device_array);
> > > > > > +
> > > > > > +static bool acpi_processor_set_per_cpu(struct acpi_processor *pr,
> > > > > > +                                struct acpi_device *device)
> > > > > > +{
> > > > > > + BUG_ON(pr->id >= nr_cpu_ids);
> > > > >
> > > > > One blank line after BUG_ON() if we need to follow original implementation.
> > > >
> > > > Sure unintentional - I'll put that back.
> > > >
> > > > >
> > > > > > + /*
> > > > > > +  * Buggy BIOS check.
> > > > > > +  * ACPI id of processors can be reported wrongly by the BIOS.
> > > > > > +  * Don't trust it blindly
> > > > > > +  */
> > > > > > + if (per_cpu(processor_device_array, pr->id) != NULL &&
> > > > > > +     per_cpu(processor_device_array, pr->id) != device) {
> > > > > > +         dev_warn(&device->dev,
> > > > > > +                  "BIOS reported wrong ACPI id %d for the processor\n",
> > > > > > +                  pr->id);
> > > > > > +         /* Give up, but do not abort the namespace scan. */
> > > > >
> > > > > It depends on how the return value is handled by the caller if the namespace
> > > > > is continued to be scanned. The caller can be acpi_processor_hotadd_init()
> > > > > and acpi_processor_get_info() after this patch is applied. So I think this
> > > > > specific comment need to be moved to the caller.
> > > >
> > > > Good point. This gets messy and was an unintended change.
> > > >
> > > > Previously the options were:
> > > > 1) acpi_processor_get_info() failed for other reasons - this code was never called.
> > > > 2) acpi_processor_get_info() succeeded without acpi_processor_hotadd_init (non hotplug)
> > > >    this code then ran and would paper over the problem doing a bunch of cleanup under err.
> > > > 3) acpi_processor_get_info() succeeded with acpi_processor_hotadd_init called.
> > > >    This code then ran and would paper over the problem doing a bunch of cleanup under err.
> > > >
> > > > We should maintain that or argue cleanly against it.
> > > >
> > > > This isn't helped the the fact I have no idea which cases we care about for that bios
> > > > bug handling.  Do any of those bios's ever do hotplug?  Guess we have to try and maintain
> > > > whatever protection this was offering.
> > > >
> > > > Also, the original code leaks data in some paths and I have limited idea
> > > > of whether it is intentional or not. So to tidy the issue up that you've identified
> > > > I'll need to try and make that code consistent first.
> > > >
> > > > I suspect the only way to do that is going to be to duplicate the allocations we
> > > > 'want' to leak to deal with the bios bug detection.
> > > >
> > > > For example acpi_processor_get_info() failing leaks pr and pr->throttling.shared_cpu_map
> > > > before this series. After this series we need pr to leak because it's used for the detection
> > > > via processor_device_array.
> > > >
> > > > I'll work through this but it's going to be tricky to tell if we get right.
> > > > Step 1 will be closing the existing leaks and then we will have something
> > > > consistent to build on.
> > > >
> > > I 'think' that fixing the original leaks makes this all much more straight forward.
> > > That return 0 for acpi_processor_get_info() never made sense as far as I can tell.
> > > The pr isn't used after this point.
> > >
> > > What about something along lines of.
> > >
> > > diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
> > > index 161c95c9d60a..97cff4492304 100644
> > > --- a/drivers/acpi/acpi_processor.c
> > > +++ b/drivers/acpi/acpi_processor.c
> > > @@ -392,8 +392,10 @@ static int acpi_processor_add(struct acpi_device *device,
> > >         device->driver_data = pr;
> > >
> > >         result = acpi_processor_get_info(device);
> > > -       if (result) /* Processor is not physically present or unavailable */
> > > -               return 0;
> > > +       if (result) { /* Processor is not physically present or unavailable */
> > > +               result = 0;
> >
> > As per my previous message (just sent) this should be an error code,
> > as returning 0 from acpi_processor_add() is generally problematic.
> Ok. I'll switch to that, but as a separate precusor patch. Independent of
> the memory leak fixes.

Sure, thank you!