cxl/acpi: Add root device lockdep validation

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.

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, however device_set_lock_class() still needs
#ifdef CONFIG_PROVE_LOCKING since lockdep_match_class() explicitly does
not have a helper in the CONFIG_PROVE_LOCKING=n case (see comment in
lockdep.h). The lockdep API needs 2 small tweaks to prevent "unused"
warnings for the @key argument to lock_set_class(), and a new
lock_set_novalidate_class() is added to supplement
lockdep_set_novalidate_class() in the cases where the lock class is
converted while the lock is held.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Alison Schofield <alison.schofield@intel.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Ben Widawsky <ben.widawsky@intel.com>
Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Link: https://lore.kernel.org/r/165100081305.1528964.11138612430659737238.stgit@dwillia2-desk3.amr.corp.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index 467b94257105..43b0dc6a0b21 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -290,6 +290,9 @@ extern void lock_set_class(struct lockdep_map *lock, const char *name,
 			   struct lock_class_key *key, unsigned int subclass,
 			   unsigned long ip);
 
+#define lock_set_novalidate_class(l, n, i) \
+	lock_set_class(l, n, &__lockdep_no_validate__, 0, i)
+
 static inline void lock_set_subclass(struct lockdep_map *lock,
 		unsigned int subclass, unsigned long ip)
 {
@@ -357,7 +360,8 @@ static inline void lockdep_set_selftest_task(struct task_struct *task)
 # define lock_acquire(l, s, t, r, c, n, i)	do { } while (0)
 # define lock_release(l, i)			do { } while (0)
 # define lock_downgrade(l, i)			do { } while (0)
-# define lock_set_class(l, n, k, s, i)		do { } while (0)
+# define lock_set_class(l, n, key, s, i)	do { (void)(key); } while (0)
+# define lock_set_novalidate_class(l, n, i)	do { } while (0)
 # define lock_set_subclass(l, s, i)		do { } while (0)
 # define lockdep_init()				do { } while (0)
 # define lockdep_init_map_type(lock, name, key, sub, inner, outer, type) \