[077/181] mm/memremap.c: convert devmap static branch to {inc,dec}

Commit Message

Andrew Morton Oct. 13, 2020, 11:52 p.m. UTC

From: Ira Weiny <[e-mail]>
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/[e-mail]/

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ira Weiny <[e-mail]>
Reviewed-by: William Kucharski <[e-mail]>
Cc: Dan Williams <[e-mail]>
Cc: Vishal Verma <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/memremap.c |    7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

Patch

--- 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