Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Content-Type: text/plain;
        charset=us-ascii
Mime-Version: 1.0 (Mac OS X Mail 14.0 \(3652.0.5.2.1\))
Subject: Re: [PATCH] memremap: Convert devmap static branch to {inc,dec}
From:   William Kucharski <william.kucharski@oracle.com>
In-Reply-To: <20200810235319.2796597-1-ira.weiny@intel.com>
Date:   Tue, 11 Aug 2020 05:59:14 -0600
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Vishal Verma <vishal.l.verma@intel.com>,
        Dan Williams <dan.j.williams@intel.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Content-Transfer-Encoding: quoted-printable
Message-Id: <4AF6A6E6-A098-448A-9CFD-86231D46032B@oracle.com>
References: <20200810235319.2796597-1-ira.weiny@intel.com>
To:     Ira Weiny <ira.weiny@intel.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Looks good to me.

Reviewed-by: William Kucharski <william.kucharski@oracle.com>

> On Aug 10, 2020, at 5:53 PM, ira.weiny@intel.com wrote:
>=20
> From: Ira Weiny <ira.weiny@intel.com>
>=20
> 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]
>=20
> 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.
>=20
> [1] =
https://lore.kernel.org/lkml/20200714194031.GI5523@worktop.programming.kic=
ks-ass.net/
>=20
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: 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(-)
>=20
> 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;
>=20
> 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);
> }
>=20
> 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;
> 	}
>=20
> -	if (atomic_inc_return(&devmap_managed_enable) =3D=3D 1)
> -		static_branch_enable(&devmap_managed_key);
> +	static_branch_inc(&devmap_managed_key);
> 	return 0;
> }
> #else
> --=20
> 2.28.0.rc0.12.gb6a658bd00c9
>=20
>=20