Re: [PATCH v2 4/4] mm, madvise: use standard madvise locking in madvise_set_anon_name()

[Lorenzo Stoakes]

On Tue, Jun 24, 2025 at 03:03:48PM +0200, Vlastimil Babka wrote:
> Use madvise_lock()/madvise_unlock() in madvise_set_anon_name() in the
> same way as in do_madvise(). This narrows the lock scope a bit and
> reuses existing functionality. get_lock_mode() already picks the correct
> MADVISE_MMAP_WRITE_LOCK mode for __MADV_SET_ANON_VMA_NAME so we can just
> remove the explicit assignment.
>
> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>

This is a nice idea, hadn't thought of it :) aren't we making anon vma name
behave now :P

I mean this is a _minor_ difference in functionality in that we will now
use mmap_write_lock_killable() and could fail to lock on fatal signal
whereas before we unconditionally lock but I think that's fine, and
possibly even... desirable actually?

At any rate this is all nice, thanks again!

> ---
>  mm/madvise.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/mm/madvise.c b/mm/madvise.c
> index cae064479cdf908707c45b941bd03d43d095eab6..ee02ccd0315a146cdb3001cd189e03be9e48a2ea 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -2082,10 +2082,10 @@ static int madvise_set_anon_name(struct mm_struct *mm, unsigned long start,
>  {
>  	unsigned long end;
>  	unsigned long len;
> +	int error;
>  	struct madvise_behavior madv_behavior = {
>  		.mm = mm,
>  		.behavior = __MADV_SET_ANON_VMA_NAME,
> -		.lock_mode = MADVISE_MMAP_WRITE_LOCK,
>  		.anon_name = anon_name,
>  	};
>
> @@ -2106,7 +2106,14 @@ static int madvise_set_anon_name(struct mm_struct *mm, unsigned long start,
>
>  	madv_behavior.range.start = start;
>  	madv_behavior.range.end = end;
> -	return madvise_walk_vmas(&madv_behavior);
> +
> +	error = madvise_lock(&madv_behavior);
> +	if (error)
> +		return error;
> +	error = madvise_walk_vmas(&madv_behavior);
> +	madvise_unlock(&madv_behavior);
> +
> +	return error;
>  }
>
>  int set_anon_vma_name(unsigned long addr, unsigned long size,
> @@ -2136,9 +2143,7 @@ int set_anon_vma_name(unsigned long addr, unsigned long size,
>  			return -ENOMEM;
>  	}
>
> -	mmap_write_lock(mm);
>  	error = madvise_set_anon_name(mm, addr, size, anon_name);
> -	mmap_write_unlock(mm);
>  	anon_vma_name_put(anon_name);
>
>  	return error;
>
> --
> 2.50.0
>