damon_ctx->call_controls_obsolete is used to disallow damon_call() requests when the request cannot be served. The field is unset and set when the context execution is started and terminated, respectively. The intention is to allow damon_call() requests only while the context is actively being executed. damon_ctx constructor, damon_new_ctx() unsets the field, though. As a result, passing the damon_ctx parameter that never successfully damon_start()-ed to damon_call() can indefinitely hang. The callers should ensure to avoid the case. Such parameter validation is not always simple. Actually such bugs in DAMON_RECLAIM and DAMON_LRU_SORT have been found and fixed [1]. Set the field in damon_new_ctx(), so that DAMON API callers can pass the context parameter to damon_call() without the additional check. [1] https://lore.kernel.org/20260803134646.16640-1-sj@kernel.org Signed-off-by: SJ Park --- 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 5882f9c94c47f..5a92e4fac6d92 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -920,6 +920,7 @@ struct damon_ctx *damon_new_ctx(void) INIT_LIST_HEAD(&ctx->adaptive_targets); INIT_LIST_HEAD(&ctx->schemes); + ctx->call_controls_obsolete = true; prandom_seed_state(&ctx->rnd_state, get_random_u64()); return ctx; @@ -2178,10 +2179,6 @@ int damon_kdamond_pid(struct damon_ctx *ctx) * synchronization. The return value of the function will be saved in * &damon_call_control->return_code. * - * 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. - * * When this function is failed, the @ctx is guaranteed to be stopped. * * Return: 0 on success, negative error code otherwise. -- 2.47.3