cleanup: Introduce ACQUIRE() and ACQUIRE_ERR() for conditional locks

scoped_cond_guard(), automatic cleanup for conditional locks, has a couple
pain points:

* It causes existing straight-line code to be re-indented into a new
  bracketed scope. While this can be mitigated by a new helper function
  to contain the scope, that is not always a comfortable conversion.

* The return code from the conditional lock is tossed in favor of a scheme
  to pass a 'return err;' statement to the macro.

Other attempts to clean this up, to behave more like guard() [1], got hung
up trying to both establish and evaluate the conditional lock in one
statement.

ACQUIRE() solves this by reflecting the result of the condition in the
automatic variable established by the lock CLASS(). The result is
separately retrieved with the ACQUIRE_ERR() helper, effectively a PTR_ERR()
operation.

Link: http://lore.kernel.org/all/Z1LBnX9TpZLR5Dkf@gmail.com [1]
Link: http://patch.msgid.link/20250512105026.GP4439@noisy.programming.kicks-ass.net
Link: http://patch.msgid.link/20250512185817.GA1808@noisy.programming.kicks-ass.net


Cc: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: David Lechner <dlechner@baylibre.com>
Cc: Fabio M. De Francesco <fabio.m.de.francesco@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
[djbw: wrap Peter's proposal with changelog and comments]
Co-developed-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Link: https://patch.msgid.link/20250711234932.671292-2-dan.j.williams@intel.com


Signed-off-by: Dave Jiang <dave.jiang@intel.com>