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

["David Hildenbrand (Arm)" <david@kernel.org>]

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