mm/damon/core: introduce damon_call_control->dealloc_on_cancel

Patch series "mm/damon/sysfs: fix refresh_ms control overwriting on
multi-kdamonds usages".

Automatic esssential DAMON/DAMOS status update feature of DAMON sysfs
interface (refresh_ms) is broken [1] for multiple DAMON contexts
(kdamonds) use case, since it uses a global single damon_call_control
object for all created DAMON contexts.  The fields of the object,
particularly the list field is over-written for the contexts and it makes
unexpected results including user-space hangup and kernel crashes [2]. 
Fix it by extending damon_call_control for the use case and updating the
usage on DAMON sysfs interface to use per-context dynamically allocated
damon_call_control object.


This patch (of 2):

When damon_call_control->repeat is set, damon_call() is executed
asynchronously, and is eventually canceled when kdamond finishes.  If the
damon_call_control object is dynamically allocated, finding the place to
deallocate the object is difficult.  Introduce a new damon_call_control
field, namely dealloc_on_cancel, to ask the kdamond deallocates those
dynamically allocated objects when those are canceled.

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Fixes: d809a7c ("mm/damon/sysfs: implement refresh_ms file internal work")
Signed-off-by: SeongJae Park <[email protected]>
Cc: Yunjeong Mun <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: sjp38

include/linux/damon.h

@@ -636,6 +636,7 @@ struct damon_operations {
  * @data:		Data that will be passed to @fn.
  * @repeat:		Repeat invocations.
  * @return_code:	Return code from @fn invocation.
+ * @dealloc_on_cancel:	De-allocate when canceled.
  *
  * Control damon_call(), which requests specific kdamond to invoke a given
  * function.  Refer to damon_call() for more details.
@@ -645,6 +646,7 @@ struct damon_call_control {
 	void *data;
 	bool repeat;
 	int return_code;
+	bool dealloc_on_cancel;
 /* private: internal use only */
 	/* informs if the kdamond finished handling of the request */
 	struct completion completion;

mm/damon/core.c

@@ -2479,10 +2479,14 @@ static void kdamond_call(struct damon_ctx *ctx, bool cancel)
 		mutex_lock(&ctx->call_controls_lock);
 		list_del(&control->list);
 		mutex_unlock(&ctx->call_controls_lock);
-		if (!control->repeat)
+		if (!control->repeat) {
 			complete(&control->completion);
-		else
+		} else if (control->canceled && control->dealloc_on_cancel) {
+			kfree(control);
+			continue;
+		} else {
 			list_add(&control->list, &repeat_controls);
+		}
 	}
 	control = list_first_entry_or_null(&repeat_controls,
 			struct damon_call_control, list);