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From: ira.weiny@intel.com
To: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	Andy Lutomirski <luto@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>
Cc: Ira Weiny <ira.weiny@intel.com>,
	x86@kernel.org, Dave Hansen <dave.hansen@linux.intel.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Vishal Verma <vishal.l.verma@intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Fenghua Yu <fenghua.yu@intel.com>,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-nvdimm@lists.01.org, linux-fsdevel@vger.kernel.org,
	linux-mm@kvack.org, linux-kselftest@vger.kernel.org
Subject: [PATCH RFC V2 09/17] memremap: Convert devmap static branch to {inc,dec}
Date: Fri, 17 Jul 2020 00:20:48 -0700
Message-ID: <20200717072056.73134-10-ira.weiny@intel.com> (raw)
In-Reply-To: <20200717072056.73134-1-ira.weiny@intel.com>

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


  parent reply index

Thread overview: 73+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-17  7:20 [PATCH RFC V2 00/17] PKS: Add Protection Keys Supervisor (PKS) support ira.weiny
2020-07-17  7:20 ` [PATCH RFC V2 01/17] x86/pkeys: Create pkeys_internal.h ira.weiny
2020-07-17  7:20 ` [PATCH RFC V2 02/17] x86/fpu: Refactor arch_set_user_pkey_access() for PKS support ira.weiny
2020-07-17  8:54   ` Peter Zijlstra
2020-07-17 20:52     ` Ira Weiny
2020-07-20  9:14       ` Peter Zijlstra
2020-07-17 22:36     ` Dave Hansen
2020-07-20  9:13       ` Peter Zijlstra
2020-07-17  7:20 ` [PATCH RFC V2 03/17] x86/pks: Enable Protection Keys Supervisor (PKS) ira.weiny
2020-07-17  7:20 ` [PATCH RFC V2 04/17] x86/pks: Preserve the PKRS MSR on context switch ira.weiny
2020-07-17  8:31   ` Peter Zijlstra
2020-07-17 21:39     ` Ira Weiny
2020-07-17  8:59   ` Peter Zijlstra
2020-07-17 22:34     ` Ira Weiny
2020-07-20  9:15       ` Peter Zijlstra
2020-07-20 18:35         ` Ira Weiny
2020-07-17  7:20 ` [PATCH RFC V2 05/17] x86/pks: Add PKS kernel API ira.weiny
2020-07-17  7:20 ` [PATCH RFC V2 06/17] x86/pks: Add a debugfs file for allocated PKS keys ira.weiny
2020-07-17  7:20 ` [PATCH RFC V2 07/17] Documentation/pkeys: Update documentation for kernel pkeys ira.weiny
2020-07-17  7:20 ` [PATCH RFC V2 08/17] x86/pks: Add PKS Test code ira.weiny
2020-07-17  7:20 ` ira.weiny [this message]
2020-07-17  7:20 ` [PATCH RFC V2 10/17] fs/dax: Remove unused size parameter ira.weiny
2020-07-17  7:20 ` [PATCH RFC V2 11/17] drivers/dax: Expand lock scope to cover the use of addresses ira.weiny
2020-07-17  7:20 ` [PATCH RFC V2 12/17] memremap: Add zone device access protection ira.weiny
2020-07-17  9:10   ` Peter Zijlstra
2020-07-18  5:06     ` Ira Weiny
2020-07-20  9:16       ` Peter Zijlstra
2020-07-17  9:17   ` Peter Zijlstra
2020-07-18  5:51     ` Ira Weiny
2020-07-17  9:20   ` Peter Zijlstra
2020-07-17  7:20 ` [PATCH RFC V2 13/17] kmap: Add stray write protection for device pages ira.weiny
2020-07-17  9:21   ` Peter Zijlstra
2020-07-19  4:13     ` Ira Weiny
2020-07-20  9:17       ` Peter Zijlstra
2020-07-21 16:31         ` Ira Weiny
2020-07-17  7:20 ` [PATCH RFC V2 14/17] dax: Stray write protection for dax_direct_access() ira.weiny
2020-07-17  9:22   ` Peter Zijlstra
2020-07-19  4:41     ` Ira Weiny
2020-07-17  7:20 ` [PATCH RFC V2 15/17] nvdimm/pmem: Stray write protection for pmem->virt_addr ira.weiny
2020-07-17  7:20 ` [PATCH RFC V2 16/17] [dax|pmem]: Enable stray write protection ira.weiny
2020-07-17  9:25   ` Peter Zijlstra
2020-07-17  7:20 ` [PATCH RFC V2 17/17] x86/entry: Preserve PKRS MSR across exceptions ira.weiny
2020-07-17  9:30   ` Peter Zijlstra
2020-07-21 18:01     ` Ira Weiny
2020-07-21 19:11       ` Peter Zijlstra
2020-07-17  9:34   ` Peter Zijlstra
2020-07-17 10:06   ` Peter Zijlstra
2020-07-22  5:27     ` Ira Weiny
2020-07-22  9:48       ` Peter Zijlstra
2020-07-22 21:24         ` Ira Weiny
2020-07-23 20:08       ` Thomas Gleixner
2020-07-23 20:15         ` Thomas Gleixner
2020-07-24 17:23           ` Ira Weiny
2020-07-24 17:29             ` Andy Lutomirski
2020-07-24 19:43               ` Ira Weiny
2020-07-22 16:21   ` Andy Lutomirski
2020-07-23 16:18     ` Fenghua Yu
2020-07-23 16:23       ` Dave Hansen
2020-07-23 16:52         ` Fenghua Yu
2020-07-23 17:08           ` Andy Lutomirski
2020-07-23 17:30             ` Dave Hansen
2020-07-23 20:23               ` Thomas Gleixner
2020-07-23 20:22             ` Thomas Gleixner
2020-07-23 21:30               ` Andy Lutomirski
2020-07-23 22:14                 ` Thomas Gleixner
2020-07-23 19:53   ` Thomas Gleixner
2020-07-23 22:04     ` Ira Weiny
2020-07-23 23:41       ` Thomas Gleixner
2020-07-24 21:24         ` Thomas Gleixner
2020-07-24 21:31           ` Thomas Gleixner
2020-07-25  0:09           ` Andy Lutomirski
2020-07-27 20:59           ` Ira Weiny
2020-07-24 22:19 ` [PATCH RFC V2 00/17] PKS: Add Protection Keys Supervisor (PKS) support Kees Cook

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