[RFC PATCH v2 04/10] mm/damon/core: set damon_ctx->walk_control_obsolete in damon_new_ctx()

[SJ Park <sj@kernel.org>]

damos_walk() should be called for a damon_ctx context that has
successfully started at least once.  That's because
damon_ctx->walk_control_obsolete is initialized when kdamond starts.  If
the rule is violated, an indefinite wait can happen.  There is no
existing violation of the rule.

damon_call() had a similar rule, and it turned out keeping the rule is
not easy for damon_call()'s case.  Hence, commit 8023b5f47e09
("mm/damon/core: set ctx->call_controls_obsolete in damon_new_ctx()")
added the initialization in damon_new_ctx() and removed the rule.

Keeping the rule for damos_walk() is relatively easier.  But having
slightly different rules for similar functions could be confusing.
Sashiko, for example, repeatedly asked questions about this.  Do the
initialization of walk_control_obsolete in damon_new_ctx() for
consistency.

[1] https://lore.kernel.org/20260915011614.102342-1-sj@kernel.org

Signed-off-by: SJ Park <sj@kernel.org>
---
 mm/damon/core.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 7bbbd44379301..9120a1b707b24 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -939,6 +939,7 @@ struct damon_ctx *damon_new_ctx(void)
 	INIT_LIST_HEAD(&ctx->schemes);
 
 	ctx->call_controls_obsolete = true;
+	ctx->walk_control_obsolete = true;
 	prandom_seed_state(&ctx->rnd_state, get_random_u64());
 
 	return ctx;
@@ -2308,10 +2309,6 @@ int damon_call(struct damon_ctx *ctx, struct damon_call_control *control)
  * passed at least one &damos->apply_interval_us, kdamond marks the request as
  * completed so that damos_walk() can wakeup and return.
  *
- * Note that this function should be called only after damon_start() with the
- * @ctx has succeeded.  Otherwise, this function could fall into an indefinite
- * wait.
- *
  * Return: 0 on success, negative error code otherwise.
  */
 int damos_walk(struct damon_ctx *ctx, struct damos_walk_control *control)
-- 
2.47.3