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mm/memremap.c: convert devmap static branch to {inc,dec} 

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/

Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Link: https://lkml.kernel.org/r/20200810235319.2796597-1-ira.weiny@intel.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Ira Weiny 2020-10-13 16:52:33 -07:00 committed by Linus Torvalds
parent 822bca52ee
commit 433e7d3177
1 changed files with 2 additions and 5 deletions
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7
mm/memremap.c
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@ -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