On Thu, Apr 21, 2022 at 08:33:18AM -0700, Dan Williams wrote: > The CXL "root" device, ACPI0017, is an attach point for coordinating > platform level CXL resources and is the parent device for a CXL port > topology tree. As such it has distinct locking rules relative to other > CXL subsystem objects, but because it is an ACPI device the lock class > is established well before it is given to the cxl_acpi driver. This final sentence gave me pause because it implied that the device lock class was set to something other than no validate. But I don't see that anywhere in the acpi code. So given that it looks to me like ACPI is just using the default no validate class...
Reviewed-by: Ira Weiny <ira.we...@intel.com> > However, the lockdep API does support changing the lock class "live" for > situations like this. Add a device_lock_set_class() helper that a driver > can use in ->probe() to set a custom lock class, and > device_lock_reset_class() to return to the default "no validate" class > before the custom lock class key goes out of scope after ->remove(). > > Note the helpers are all macros to support dead code elimination in the > CONFIG_PROVE_LOCKING=n case. > > Suggested-by: Peter Zijlstra <pet...@infradead.org> > Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org> > Cc: "Rafael J. Wysocki" <raf...@kernel.org> > Cc: Ingo Molnar <mi...@redhat.com> > Cc: Will Deacon <w...@kernel.org> > Cc: Waiman Long <long...@redhat.com> > Cc: Boqun Feng <boqun.f...@gmail.com> > Cc: Alison Schofield <alison.schofi...@intel.com> > Cc: Vishal Verma <vishal.l.ve...@intel.com> > Cc: Ira Weiny <ira.we...@intel.com> > Cc: Ben Widawsky <ben.widaw...@intel.com> > Cc: Jonathan Cameron <jonathan.came...@huawei.com> > Signed-off-by: Dan Williams <dan.j.willi...@intel.com> > --- > drivers/cxl/acpi.c | 15 +++++++++++++++ > include/linux/device.h | 25 +++++++++++++++++++++++++ > 2 files changed, 40 insertions(+) > > diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c > index d15a6aec0331..e19cea27387e 100644 > --- a/drivers/cxl/acpi.c > +++ b/drivers/cxl/acpi.c > @@ -275,6 +275,15 @@ static int add_root_nvdimm_bridge(struct device *match, > void *data) > return 1; > } > > +static struct lock_class_key cxl_root_key; > + > +static void cxl_acpi_lock_reset_class(void *_dev) > +{ > + struct device *dev = _dev; > + > + device_lock_reset_class(dev); > +} > + > static int cxl_acpi_probe(struct platform_device *pdev) > { > int rc; > @@ -283,6 +292,12 @@ static int cxl_acpi_probe(struct platform_device *pdev) > struct acpi_device *adev = ACPI_COMPANION(host); > struct cxl_cfmws_context ctx; > > + device_lock_set_class(&pdev->dev, &cxl_root_key); > + rc = devm_add_action_or_reset(&pdev->dev, cxl_acpi_lock_reset_class, > + &pdev->dev); > + if (rc) > + return rc; > + > root_port = devm_cxl_add_port(host, host, CXL_RESOURCE_NONE, NULL); > if (IS_ERR(root_port)) > return PTR_ERR(root_port); > diff --git a/include/linux/device.h b/include/linux/device.h > index 93459724dcde..82c9d307e7bd 100644 > --- a/include/linux/device.h > +++ b/include/linux/device.h > @@ -850,6 +850,31 @@ static inline bool device_supports_offline(struct device > *dev) > return dev->bus && dev->bus->offline && dev->bus->online; > } > > +#define __device_lock_set_class(dev, name, key) \ > + lock_set_class(&(dev)->mutex.dep_map, name, key, 0, _THIS_IP_) > + > +/** > + * device_lock_set_class - Specify a temporary lock class while a device > + * is attached to a driver > + * @dev: device to modify > + * @key: lock class key data > + * > + * This must be called with the device_lock() already held, for example > + * from driver ->probe(). > + */ > +#define device_lock_set_class(dev, key) \ > + __device_lock_set_class(dev, #key, key) > + > +/** > + * device_lock_reset_class - Return a device to the default lockdep > novalidate state > + * @dev: device to modify > + * > + * This must be called with the device_lock() already held, for example > + * from driver ->remove(). > + */ > +#define device_lock_reset_class(dev) \ > + device_lock_set_class(dev, &__lockdep_no_validate__) > + > void lock_device_hotplug(void); > void unlock_device_hotplug(void); > int lock_device_hotplug_sysfs(void); >