[PATCH v3] mm/khugepaged: replace mutex_lock/mutex_unlock usage with guard macro

[Jakov Novak <jakovnovak30@gmail.com>]

Currently, khugepaged locks the khugepaged_mutex in two functions:
start_stop_khugepaged and khugepaged_min_free_kbytes_update. Remove
mutex_lock/mutex_unlock usage in these functions and replace it with the
guard macro. This makes the code more readable (removing a goto statement)
and makes it harder to introduce bugs in the future.
No functional changes introduced.

Signed-off-by: Jakov Novak <jakovnovak30@gmail.com>
Reviewed-by: Dev Jain <dev.jain@arm.com>
Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Zi Yan <ziy@nvidia.com>
---
v2:
  - Added #include <linux/cleanup.h> to the includes at the top of the file
  - Moved err declaration to the scope where it's used in
    start_stop_khugepaged
  - Made default case return 0 instead of err in start_stop_khugepaged
v3:
  - Moved new thread creation logic inside if (!khugepaged_thread) block
    in start_stop_khugepaged
  - Removed suboptimal err variable

 mm/khugepaged.c | 31 +++++++++++++++----------------
 1 file changed, 15 insertions(+), 16 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 617bca76db49..97f61a050f7c 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -23,6 +23,7 @@
 #include <linux/ksm.h>
 #include <linux/pgalloc.h>
 #include <linux/backing-dev.h>
+#include <linux/cleanup.h>
 
 #include <asm/tlb.h>
 #include "internal.h"
@@ -3111,18 +3112,19 @@ void set_recommended_min_free_kbytes(void)
 
 int start_stop_khugepaged(void)
 {
-	int err = 0;
-
-	mutex_lock(&khugepaged_mutex);
+	guard(mutex)(&khugepaged_mutex);
 	if (hugepage_enabled()) {
-		if (!khugepaged_thread)
-			khugepaged_thread = kthread_run(khugepaged, NULL,
-							"khugepaged");
-		if (IS_ERR(khugepaged_thread)) {
-			pr_err("khugepaged: kthread_run(khugepaged) failed\n");
-			err = PTR_ERR(khugepaged_thread);
-			khugepaged_thread = NULL;
-			goto fail;
+		if (!khugepaged_thread) {
+			struct task_struct *new_thread = kthread_run(khugepaged,
+								     NULL,
+								     "khugepaged");
+
+			if (IS_ERR(new_thread)) {
+				pr_err("khugepaged: kthread_run(khugepaged) failed\n");
+				return PTR_ERR(new_thread);
+			}
+
+			khugepaged_thread = new_thread;
 		}
 
 		if (!list_empty(&khugepaged_scan.mm_head))
@@ -3132,17 +3134,14 @@ int start_stop_khugepaged(void)
 		khugepaged_thread = NULL;
 	}
 	set_recommended_min_free_kbytes();
-fail:
-	mutex_unlock(&khugepaged_mutex);
-	return err;
+	return 0;
 }
 
 void khugepaged_min_free_kbytes_update(void)
 {
-	mutex_lock(&khugepaged_mutex);
+	guard(mutex)(&khugepaged_mutex);
 	if (hugepage_enabled() && khugepaged_thread)
 		set_recommended_min_free_kbytes();
-	mutex_unlock(&khugepaged_mutex);
 }
 
 bool current_is_khugepaged(void)
-- 
2.55.0