2020-08-10 23:54:17

by Ira Weiny

Subject: [PATCH] memremap: Convert devmap static branch to {inc,dec}

From: Ira Weiny <[email protected]>

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/[email protected]/

Cc: Dan Williams <[email protected]>
Cc: Vishal Verma <[email protected]>
Signed-off-by: Ira Weiny <[email protected]>
---
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

2020-08-11 12:03:28

by William Kucharski

Subject: Re: [PATCH] memremap: Convert devmap static branch to {inc,dec}

Looks good to me.

Reviewed-by: William Kucharski <[email protected]>

> On Aug 10, 2020, at 5:53 PM, [email protected] wrote:
>
> From: Ira Weiny <[email protected]>
>
> 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/[email protected]/
>
> Cc: Dan Williams <[email protected]>
> Cc: Vishal Verma <[email protected]>
> Signed-off-by: Ira Weiny <[email protected]>
> ---
> 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
>
>