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 mistake, and indeed a few bugs from such mistakes were found and fixed.

Refactor the core API functions to stop all contexts to avoid the mistakes. Also remove the unnecessary error handlings from callers.

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 stop the context before returning the error. Patches 10 and 11 remove unnecessary error handlings from callers (wsse and prcl sample modules).

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: stop ctx 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, 32 insertions(+), 35 deletions(-)

base-commit: 39f9f608b1858e65db6d2766d692a7a700b1e0fb

2.47.3