[PATCH RFC V2 09/17] memremap: Convert devmap static branch to {inc,dec}

ira.weiny
2020-07-17T07:21:16Z

From: Ira Weiny <ira.weiny@intel.com>

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@worktop.programming.kicks-ass.net/

To: Dan Williams <dan.j.williams@intel.com>
To: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
---
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