linux-kernel - Re: [PATCH 05/11] cxl/core: Introduce cxl_set_lock

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Date:   Wed, 9 Mar 2022 20:08:43 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Rafael J Wysocki <rafael.j.wysocki@...el.com>,
        Alison Schofield <alison.schofield@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Ben Widawsky <ben.widawsky@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-cxl@...r.kernel.org, Linux NVDIMM <nvdimm@...ts.linux.dev>
Subject: Re: [PATCH 05/11] cxl/core: Introduce cxl_set_lock_class()

On Wed, Mar 9, 2022 at 10:33 AM Jonathan Cameron
<Jonathan.Cameron@...wei.com> wrote:
>
> On Mon, 28 Feb 2022 18:49:17 -0800
> Dan Williams <dan.j.williams@...el.com> wrote:
>
> > Update CONFIG_PROVE_CXL_LOCKING to use the common device-core helpers
> > for device_lock validation.
> >
> > When CONFIG_PROVE_LOCKING is enabled and device_set_lock_class() is
> > passed a non-zero lock class the core acquires the 'struct device'
> > @lockdep_mutex everywhere it acquires the device_lock. Where
> > lockdep_mutex does not skip lockdep validation like device_lock.
> >
> > cxl_set_lock_class() wraps device_set_lock_class() as to not collide
> > with other subsystems that may also support this lockdep validation
> > scheme. See the 'choice' for the various CONFIG_PROVE_$SUBSYS_LOCKING
> > options in lib/Kconfig.debug.
> >
> > Cc: Alison Schofield <alison.schofield@...el.com>
> > Cc: Vishal Verma <vishal.l.verma@...el.com>
> > Cc: Ira Weiny <ira.weiny@...el.com>
> > Cc: Ben Widawsky <ben.widawsky@...el.com>
> > Signed-off-by: Dan Williams <dan.j.williams@...el.com>
>
> One query inline - otherwise looks good to me.
>
> > ---
>
> > diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
> > index b1a4ba622739..f0a821de94cf 100644
> > --- a/drivers/cxl/core/region.c
> > +++ b/drivers/cxl/core/region.c
> > @@ -476,6 +476,7 @@ int cxl_add_region(struct cxl_decoder *cxld, struct cxl_region *cxlr)
> >       if (rc)
> >               goto err;
> >
> > +     cxl_set_lock_class(dev);
>
> I didn't see a cxl_lock_class for regions. Or is this meant to use
> the ANON_LOCK?

Oh, yes, first I need to rebase this set before the region series
which is going through a major revision. Second, I expect that the
region lock_class may end up needing to nest inside the decoder lock
class in order to facilitate decoders disconnecting themselves from
regions if a memdev goes through ->remove() while an associated region
is active.

This series was motivated by wanting to validate the locking of the
region creation sysfs-ABI versus device removal events.