Looks good to me.
Reviewed-by: William Kucharski <william.kucharski@xxxxxxxxxx>
> On Aug 10, 2020, at 5:53 PM, ira.weiny@xxxxxxxxx wrote:
>
> From: Ira Weiny <ira.weiny@xxxxxxxxx>
>
> While reviewing Protection Key Supervisor support it was pointed out
> that using a counter to track static branch enable was an anti-pattern
> which was better solved using the provided static_branch_{inc,dec}
> functions.[1]
>
> Fix up devmap_managed_key to work the same way. Also this should be
> safer because there is a very small (very unlikely) race when multiple
> callers try to enable at the same time.
>
> [1] https://lore.kernel.org/lkml/20200714194031.GI5523@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: Vishal Verma <vishal.l.verma@xxxxxxxxx>
> Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
> ---
> mm/memremap.c | 7 ++-----
> 1 file changed, 2 insertions(+), 5 deletions(-)
>
> diff --git a/mm/memremap.c b/mm/memremap.c
> index 03e38b7a38f1..9fb9ad500e78 100644
> --- a/mm/memremap.c
> +++ b/mm/memremap.c
> @@ -40,12 +40,10 @@ EXPORT_SYMBOL_GPL(memremap_compat_align);
> #ifdef CONFIG_DEV_PAGEMAP_OPS
> DEFINE_STATIC_KEY_FALSE(devmap_managed_key);
> EXPORT_SYMBOL(devmap_managed_key);
> -static atomic_t devmap_managed_enable;
>
> static void devmap_managed_enable_put(void)
> {
> - if (atomic_dec_and_test(&devmap_managed_enable))
> - static_branch_disable(&devmap_managed_key);
> + static_branch_dec(&devmap_managed_key);
> }
>
> static int devmap_managed_enable_get(struct dev_pagemap *pgmap)
> @@ -56,8 +54,7 @@ static int devmap_managed_enable_get(struct dev_pagemap *pgmap)
> return -EINVAL;
> }
>
> - if (atomic_inc_return(&devmap_managed_enable) == 1)
> - static_branch_enable(&devmap_managed_key);
> + static_branch_inc(&devmap_managed_key);
> return 0;
> }
> #else
> --
> 2.28.0.rc0.12.gb6a658bd00c9
>
>
