Re: [PATCH v2 2/3] mm: vmalloc: Switch to find_unlink_vmap_area() in vm_unmap_ram()

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@xxxxxx>

On Wed, Dec 21, 2022 at 06:44:53PM +0100, Uladzislau Rezki (Sony) wrote:
> Switch from find_vmap_area() to find_unlink_vmap_area() to prevent
> a double access to the vmap_area_lock: one for finding area, second
> time is for unlinking from a tree.
> 
> Signed-off-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
> ---
>  mm/vmalloc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 28030d2441f1..17e688cc7357 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2251,7 +2251,7 @@ void vm_unmap_ram(const void *mem, unsigned int count)
>  		return;
>  	}
>  
> -	va = find_vmap_area(addr);
> +	va = find_unlink_vmap_area(addr);

I can't find find_unlink_vmap_area in current -next, but shouldn't
this also switch from free_vmap_area_noflush to something that
doesn't unlink from the list and avoid the lock?

In general the code could probably use a bit of refactoring to
split unmapping from freeing.