[PATCH v2] mm/khugepaged: replace mutex_lock/mutex_unlock usage with guard macro

[PATCH v2] mm/khugepaged: replace mutex_lock/mutex_unlock usage with guard macro

[Jakov Novak]

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>
---
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

 mm/khugepaged.c | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 617bca76db49..7890bd3e2a9d 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 +3112,17 @@ 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)) {
+			int err;
 			pr_err("khugepaged: kthread_run(khugepaged) failed\n");
 			err = PTR_ERR(khugepaged_thread);
 			khugepaged_thread = NULL;
-			goto fail;
+			return err;
 		}
 
 		if (!list_empty(&khugepaged_scan.mm_head))
@@ -3132,17 +3132,14 @@ 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

Re: [PATCH v2] mm/khugepaged: replace mutex_lock/mutex_unlock usage with guard macro

[Zi Yan]

On Tue Jul 28, 2026 at 4:46 PM EDT, Jakov Novak wrote:
> 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>
> ---
> 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
>
>  mm/khugepaged.c | 15 ++++++---------
>  1 file changed, 6 insertions(+), 9 deletions(-)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 617bca76db49..7890bd3e2a9d 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 +3112,17 @@ 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)) {
> +			int err;

A new line here?

>  			pr_err("khugepaged: kthread_run(khugepaged) failed\n");
>  			err = PTR_ERR(khugepaged_thread);
>  			khugepaged_thread = NULL;
> -			goto fail;
> +			return err;
>  		}
>  
>  		if (!list_empty(&khugepaged_scan.mm_head))

Otherwise, LGTM.

Reviewed-by: Zi Yan <ziy@nvidia.com>



-- 
Best Regards,
Yan, Zi

Re: [PATCH v2] mm/khugepaged: replace mutex_lock/mutex_unlock usage with guard macro

[David Hildenbrand (Arm)]

On 7/28/26 22:46, Jakov Novak wrote:
> 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>
> ---
> 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
> 
>  mm/khugepaged.c | 15 ++++++---------
>  1 file changed, 6 insertions(+), 9 deletions(-)
> 
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 617bca76db49..7890bd3e2a9d 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 +3112,17 @@ 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)) {
> +			int err;
>  			pr_err("khugepaged: kthread_run(khugepaged) failed\n");
>  			err = PTR_ERR(khugepaged_thread);
>  			khugepaged_thread = NULL;
> -			goto fail;
> +			return err;
>  		}

While at it, can we just do

struct task_struct *new_thread = kthread_run...

if (IS_ERR(new_thread)) {
	pr_err("khugepaged: kthread_run(khugepaged) failed\n");
	return PTR_ERR(new_thread);
}
khugepaged_thread = new_thread;

?

Avoid the suboptimal err variable and temporarily assigning error values to the
global variable.

-- 
Cheers,

David

Re: [PATCH v2] mm/khugepaged: replace mutex_lock/mutex_unlock usage with guard macro

[jakov novak]

I guess the error checking could be moved inside the if
(!khugepaged_thread) block like:

if (!khugepaged_thread) {
  struct task_struct *new_thread = kthread_run...

  if (IS_ERR(new_thread)) {
    pr_err...
    return PTR_ERR(new_thread);
  }

  khugepaged_thread = new_thread;
}

I can send a v3 with these changes if this looks good to everybody.

Best,
Jakov

On Wed, Jul 29, 2026 at 9:56 AM David Hildenbrand (Arm)
<david@kernel.org> wrote:
>
> On 7/28/26 22:46, Jakov Novak wrote:
> > 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>
> > ---
> > 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
> >
> >  mm/khugepaged.c | 15 ++++++---------
> >  1 file changed, 6 insertions(+), 9 deletions(-)
> >
> > diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> > index 617bca76db49..7890bd3e2a9d 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 +3112,17 @@ 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)) {
> > +                     int err;
> >                       pr_err("khugepaged: kthread_run(khugepaged) failed\n");
> >                       err = PTR_ERR(khugepaged_thread);
> >                       khugepaged_thread = NULL;
> > -                     goto fail;
> > +                     return err;
> >               }
>
> While at it, can we just do
>
> struct task_struct *new_thread = kthread_run...
>
> if (IS_ERR(new_thread)) {
>         pr_err("khugepaged: kthread_run(khugepaged) failed\n");
>         return PTR_ERR(new_thread);
> }
> khugepaged_thread = new_thread;
>
> ?
>
> Avoid the suboptimal err variable and temporarily assigning error values to the
> global variable.
>
> --
> Cheers,
>
> David

Re: [PATCH v2] mm/khugepaged: replace mutex_lock/mutex_unlock usage with guard macro

[David Hildenbrand (Arm)]

On 7/29/26 13:56, jakov novak wrote:
> I guess the error checking could be moved inside the if
> (!khugepaged_thread) block like:
> 
> if (!khugepaged_thread) {
>   struct task_struct *new_thread = kthread_run...
> 
>   if (IS_ERR(new_thread)) {
>     pr_err...
>     return PTR_ERR(new_thread);
>   }
> 
>   khugepaged_thread = new_thread;
> }
> 
> I can send a v3 with these changes if this looks good to everybody.
>

Yes, please so so.

-- 
Cheers,

David