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Tue, 11 Aug 2020 11:59:19 +0000 Received: from pps.filterd (aserp3020.oracle.com [127.0.0.1]) by aserp3020.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 07BBxHHZ067225; Tue, 11 Aug 2020 11:59:18 GMT Received: from userv0121.oracle.com (userv0121.oracle.com [156.151.31.72]) by aserp3020.oracle.com with ESMTP id 32t5y3sxg0-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 11 Aug 2020 11:59:18 +0000 Received: from abhmp0007.oracle.com (abhmp0007.oracle.com [141.146.116.13]) by userv0121.oracle.com (8.14.4/8.13.8) with ESMTP id 07BBxF0N005209; Tue, 11 Aug 2020 11:59:15 GMT Received: from localhost (/73.243.10.6) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 11 Aug 2020 11:59:15 +0000 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 In-Reply-To: <20200810235319.2796597-1-ira.weiny@intel.com> Date: Tue, 11 Aug 2020 05:59:14 -0600 Cc: Andrew Morton , Vishal Verma , Dan Williams , "Aneesh Kumar K.V" , 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 X-Mailer: Apple Mail (2.3652.0.5.2.1) X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9709 signatures=668679 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 malwarescore=0 suspectscore=0 mlxscore=0 adultscore=0 bulkscore=0 phishscore=0 mlxlogscore=999 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2008110083 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9709 signatures=668679 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 lowpriorityscore=0 bulkscore=0 impostorscore=0 phishscore=0 clxscore=1011 spamscore=0 malwarescore=0 adultscore=0 mlxlogscore=999 mlxscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2008110083 X-Rspamd-Queue-Id: 2797C28A4E8 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam05 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Looks good to me. Reviewed-by: William Kucharski > On Aug 10, 2020, at 5:53 PM, ira.weiny@intel.com wrote: >=20 > From: Ira Weiny >=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 > Cc: Vishal Verma > Signed-off-by: Ira Weiny > --- > 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