RFC mm/damon: refactor damon_{start,stop,commit}() for simple error handling

damon_start() and damon_stop() could leave a few of requested DAMON contexts running when they return an error. damon_commit() failure stops the DAMON context, but in an asynchronous way. Callers should stop the left-over DAMON contexts. It is easy to make mistakes, and indeed a few bugs from such mistakes were found and fixed.

Refactor the core API functions to guarantee contexts are completely stopped under failures. Remove the caller side error handlers that are no longer needed due to the refactoring.

Patches Sequence
================

Patch 1 refactors damon_start() to ensure all contexts are stopped for failures. Patch 2 updates unnecessary damon_start() error handling from mtier sample module.

Patch 3 refactors damon_stop() to always success. Patches 4-6 updates callers (damon_{sysfs,reclaim lru_sort}) to ignore the return value. Patch 7 update damon_stop() return value to void. Patch 8 simplifies damon_stop() error handling in mtier sample module.

Patch 9 refactors damon_call() to return errors only after the context is completely stopped. Patches 10 and 11 remove unnecessary error handlings from callers (wsse and prcl sample modules).

Changelog
=========

Changes from RFC v1
- RFC v1: https://lore.kernel.org/[email protected]
- Fix ABBA deadlock in damon_start().
- Wait instead of doing racy-stop in damon_call().

SJ Park (11):
mm/damon/core: stop ctxs in damon_start() before returning an error samples/damon/mtier: do not stop first context for damon_start()
failure
mm/damon/core: make damon_stop() never fails mm/damon/sysfs: ignore damon_stop() return value mm/damon/reclaaim: ignore damon_stop() return value mm/damon/lru_sort: ignore damon_stop() return value mm/damon/core: change damon_stop() return type to void samples/damon/mtier: stop all contexts with single damon_stop() call mm/damon/core: wait ctx stop in damon_call() before reruning an error samples/damon/wsse: do not stop ctx for damon_call() failure samples/damon/prcl: do not stop DAMON for damon_call() failure

 include/linux/damon.h |  2 +-
 mm/damon/core.c       | 37 +++++++++++++++++++------------------
 mm/damon/lru_sort.c   |  6 ++++--
 mm/damon/reclaim.c    |  6 ++++--
 mm/damon/sysfs.c      |  3 ++-
 samples/damon/mtier.c |  5 +----
 samples/damon/prcl.c  |  4 +---
 samples/damon/wsse.c  |  4 +---
 8 files changed, 33 insertions(+), 34 deletions(-)

base-commit: abe5b65a9c676375c3f118d453037f2f9ebbb7ac

2.47.3