From: Ira Weiny <ira.weiny@xxxxxxxxx>
Subject: 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@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
Link: https://lkml.kernel.org/r/20200810235319.2796597-1-ira.weiny@xxxxxxxxx
Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
Reviewed-by: William Kucharski <william.kucharski@xxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Vishal Verma <vishal.l.verma@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/memremap.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)
--- a/mm/memremap.c~memremap-convert-devmap-static-branch-to-incdec
+++ a/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(str
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
_
