mm/damon/sysfs: remove damon_sysfs_cmd_request and its readers

damon_sysfs_cmd_request is DAMON sysfs interface's own synchronization
mechanism for accessing DAMON internal data via damon_callback hooks.  All
the users are now migrated to damon_call() and damos_walk(), so nobody
really uses it.  No one writes to the data structure but reading code is
still remained.  Remove the reading code and the entire data structure.

Link: https://lkml.kernel.org/r/20250306175908.66300-8-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: sjp38

mm/damon/sysfs.c

@@ -1238,25 +1238,6 @@ static const char * const damon_sysfs_cmd_strs[] = {
 	"update_tuned_intervals",
 };
 
-/*
- * struct damon_sysfs_cmd_request - A request to the DAMON callback.
- * @cmd:	The command that needs to be handled by the callback.
- * @kdamond:	The kobject wrapper that associated to the kdamond thread.
- *
- * This structure represents a sysfs command request that need to access some
- * DAMON context-internal data.  Because DAMON context-internal data can be
- * safely accessed from DAMON callbacks without additional synchronization, the
- * request will be handled by the DAMON callback.  None-``NULL`` @kdamond means
- * the request is valid.
- */
-struct damon_sysfs_cmd_request {
-	enum damon_sysfs_cmd cmd;
-	struct damon_sysfs_kdamond *kdamond;
-};
-
-/* Current DAMON callback request.  Protected by damon_sysfs_lock. */
-static struct damon_sysfs_cmd_request damon_sysfs_cmd_request;
-
 static ssize_t state_show(struct kobject *kobj, struct kobj_attribute *attr,
 		char *buf)
 {
@@ -1555,8 +1536,6 @@ static int damon_sysfs_turn_damon_on(struct damon_sysfs_kdamond *kdamond)
 
 	if (damon_sysfs_kdamond_running(kdamond))
 		return -EBUSY;
-	if (damon_sysfs_cmd_request.kdamond == kdamond)
-		return -EBUSY;
 	/* TODO: support multiple contexts per kdamond */
 	if (kdamond->contexts->nr != 1)
 		return -EINVAL;
@@ -1796,8 +1775,7 @@ static bool damon_sysfs_kdamonds_busy(struct damon_sysfs_kdamond **kdamonds,
 	int i;
 
 	for (i = 0; i < nr_kdamonds; i++) {
-		if (damon_sysfs_kdamond_running(kdamonds[i]) ||
-		    damon_sysfs_cmd_request.kdamond == kdamonds[i])
+		if (damon_sysfs_kdamond_running(kdamonds[i]))
 			return true;
 	}