Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   "Michael Kelley (EOSG)" <Michael.H.Kelley@microsoft.com>
To:     Jia-Ju Bai <baijiaju1990@gmail.com>,
        KY Srinivasan <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        "bhelgaas@google.com" <bhelgaas@google.com>
CC:     "devel@linuxdriverproject.org" <devel@linuxdriverproject.org>,
        "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH 1/2] pci: host: pci-hyperv: Replace GFP_ATOMIC with
 GFP_KERNEL in hv_pci_onchannelcallback
Thread-Topic: [PATCH 1/2] pci: host: pci-hyperv: Replace GFP_ATOMIC with
 GFP_KERNEL in hv_pci_onchannelcallback
Thread-Index: AQHTvsja6KbTRPVg0UyrOUPXmgRmnKPWlbsA
Date:   Sun, 18 Mar 2018 22:40:55 +0000
Message-ID: <DM5PR2101MB1030145AB251BF2F31FBA4BEDCD50@DM5PR2101MB1030.namprd21.prod.outlook.com>
References: <1521384782-23539-1-git-send-email-baijiaju1990@gmail.com>
In-Reply-To: <1521384782-23539-1-git-send-email-baijiaju1990@gmail.com>
Accept-Language: en-US
Content-Language: en-US
msip_labels: MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_Enabled=True;
 MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_SiteId=72f988bf-86f1-41af-91ab-2d7cd011db47;
 MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_Owner=mikelley@ntdev.microsoft.com;
 MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_SetDate=2018-03-18T22:40:53.8933675Z;
 MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_Name=General;
 MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_Application=Microsoft Azure
 Information Protection;
 MSIP_Label_f42aa342-8706-4288-bd11-ebb85995028c_Extended_MSFT_Method=Automatic;
 Sensitivity=General
x-originating-ip: [24.22.167.197]
x-ms-publictraffictype: Email
x-microsoft-exchange-diagnostics: 1;DM5PR2101MB1080;7:hULsFqYr1fadHw1kH2RFZl4BrkyZSRWYCle6Y7CI6wJkRnIiVwRpBgUmM4p6xNDiDWMv+9hwIWNkXwp40+5tEomC3URfu3uWV3EYzO5bw4JaiT0bZ+1gmkGZnqiPcOL38Fk5Wmpf0M4LCZAI3zveRSqY2meqqu0SgkNCpWlu04Dsbo2Dey0VDhySZqbMS428pClNfjorlnKaSh2bnjr50FTu/mfZolTn6pH+9STw0CSDHEf3LKtm6NqEYqrIbrVE;20:4d87qYavPyndoIczl1KBE9b3Db3fBoQizQXah5A4i8ON0uiLRMbYhuCyObswXWB37EitTK8jfEm6+PvHh9a8ti1hKZsFoITFVXf6VBWq7T2jCKva9sRYywUxkhJceQA6GVmSLqw/4To51bCApMn7yAq99cDKBs+UapqkuhZLQpo=
x-ms-exchange-antispam-srfa-diagnostics: SOS;
x-ms-office365-filtering-ht: Tenant
x-ms-office365-filtering-correlation-id: 393bf07d-c432-4eb3-de48-08d58d214fdb
x-microsoft-antispam: UriScan:;BCL:0;PCL:0;RULEID:(7020095)(4652020)(48565401081)(5600026)(4604075)(3008032)(4534165)(4627221)(201703031133081)(201702281549075)(2017052603328)(7193020);SRVR:DM5PR2101MB1080;
x-ms-traffictypediagnostic: DM5PR2101MB1080:
authentication-results: spf=none (sender IP is )
 smtp.mailfrom=Michael.H.Kelley@microsoft.com; 
x-microsoft-antispam-prvs: <DM5PR2101MB10805D2181C42E636CFBE1ADDCD50@DM5PR2101MB1080.namprd21.prod.outlook.com>
x-exchange-antispam-report-test: UriScan:(28532068793085)(89211679590171)(9452136761055)(85827821059158)(788757137089)(211936372134217);
x-exchange-antispam-report-cfa-test: BCL:0;PCL:0;RULEID:(8211001083)(61425038)(6040522)(2401047)(8121501046)(5005006)(93006095)(93001095)(10201501046)(3231221)(944501300)(52105095)(3002001)(6055026)(61426038)(61427038)(6041310)(201703131423095)(201702281528075)(20161123555045)(201703061421075)(201703061406153)(20161123564045)(20161123562045)(20161123558120)(20161123560045)(6072148)(201708071742011);SRVR:DM5PR2101MB1080;BCL:0;PCL:0;RULEID:;SRVR:DM5PR2101MB1080;
x-forefront-prvs: 06157D541C
x-forefront-antispam-report: SFV:NSPM;SFS:(10019020)(39860400002)(39380400002)(376002)(396003)(346002)(366004)(199004)(189003)(13464003)(74316002)(5660300001)(3660700001)(2906002)(76176011)(54906003)(110136005)(53936002)(186003)(39060400002)(4326008)(6116002)(3846002)(3280700002)(99286004)(97736004)(2950100002)(316002)(106356001)(6436002)(26005)(7696005)(9686003)(6246003)(55016002)(81156014)(81166006)(8676002)(305945005)(10090500001)(10290500003)(478600001)(33656002)(1511001)(8990500004)(72206003)(22452003)(105586002)(86362001)(8936002)(86612001)(25786009)(102836004)(2501003)(5250100002)(14454004)(53546011)(6506007)(68736007)(229853002)(2900100001)(66066001)(7736002);DIR:OUT;SFP:1102;SCL:1;SRVR:DM5PR2101MB1080;H:DM5PR2101MB1030.namprd21.prod.outlook.com;FPR:;SPF:None;LANG:en;PTR:InfoNoRecords;A:1;MX:1;
received-spf: None (protection.outlook.com: microsoft.com does not designate
 permitted sender hosts)
x-microsoft-antispam-message-info: rzesWP/ruTL0lxLWfenVeP9lXowgsVY8VobsAkr4CKR0akXR78iyC3mIJYAAvRtrGwE0+GHXwO5qvJ+Z539uVR5nIis6xLjx1PUatmEuFEe4fcInO68CY/8snBhBrHx80myq2mg7p2WhJgzxerabf5UHrLY3+QmT9iPQqJdtTvVJtavrEqiCeli2gTeoZ/sfo8XghcZkGoHLME0vDbARrirhW8aP9rDfwHNetqqs5Wrxgk+2UpSNMEtSPKahAcZ88CGG2Tbc1QSX/UeLr75xU/omL9cymbJrvibYL+CtanusDhsMgyyF6G13RvoClYcrx3P7UGRtIbfmw8HjVPH+1w==
spamdiagnosticoutput: 1:99
spamdiagnosticmetadata: NSPM
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
X-OriginatorOrg: microsoft.com
X-MS-Exchange-CrossTenant-Network-Message-Id: 393bf07d-c432-4eb3-de48-08d58d214fdb
X-MS-Exchange-CrossTenant-originalarrivaltime: 18 Mar 2018 22:40:55.4068
 (UTC)
X-MS-Exchange-CrossTenant-fromentityheader: Hosted
X-MS-Exchange-CrossTenant-id: 72f988bf-86f1-41af-91ab-2d7cd011db47
X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM5PR2101MB1080
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

> -----Original Message-----
> From: linux-kernel-owner@vger.kernel.org <linux-kernel-owner@vger.kernel.=
org> On Behalf
> Of Jia-Ju Bai
> Sent: Sunday, March 18, 2018 7:53 AM
> To: KY Srinivasan <kys@microsoft.com>; Haiyang Zhang <haiyangz@microsoft.=
com>; Stephen
> Hemminger <sthemmin@microsoft.com>; bhelgaas@google.com
> Cc: devel@linuxdriverproject.org; linux-pci@vger.kernel.org; linux-kernel=
@vger.kernel.org;
> Jia-Ju Bai <baijiaju1990@gmail.com>
> Subject: [PATCH 1/2] pci: host: pci-hyperv: Replace GFP_ATOMIC with GFP_K=
ERNEL in
> hv_pci_onchannelcallback
>=20
> hv_pci_onchannelcallback() is not called in atomic context.
>=20
> The call chain ending up at hv_pci_onchannelcallback() is:
> [1] hv_pci_onchannelcallback() <- hv_pci_probe()
> hv_pci_probe() is only set as ".probe" in hv_driver
> structure "hv_pci_drv".
>=20
> Despite never getting called from atomic context,

Not true.   hv_pci_probe() registers hv_pci_onchannelcallback() as
a callback function that is invoked from the VMbus interrupt handler.
So GFP_ATOMIC is appropriate.

Michael

> hv_pci_onchannelcallback() calls kmalloc with GFP_ATOMIC,
> which waits busily for allocation.
> GFP_ATOMIC is not necessary and can be replaced with GFP_KERNEL
> to avoid busy waiting.
>=20
> This is found by a static analysis tool named DCNS written by myself.
>=20
> Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
> ---
>  drivers/pci/host/pci-hyperv.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>=20
> diff --git a/drivers/pci/host/pci-hyperv.c b/drivers/pci/host/pci-hyperv.=
c
> index 0fe3ea1..c5c8a99 100644
> --- a/drivers/pci/host/pci-hyperv.c
> +++ b/drivers/pci/host/pci-hyperv.c
> @@ -1887,7 +1887,7 @@ static void hv_pci_onchannelcallback(void *context)
>  	struct pci_dev_incoming *dev_message;
>  	struct hv_pci_dev *hpdev;
>=20
> -	buffer =3D kmalloc(bufferlen, GFP_ATOMIC);
> +	buffer =3D kmalloc(bufferlen, GFP_KERNEL);
>  	if (!buffer)
>  		return;
>=20
> @@ -1899,7 +1899,7 @@ static void hv_pci_onchannelcallback(void *context)
>  			kfree(buffer);
>  			/* Handle large packet */
>  			bufferlen =3D bytes_recvd;
> -			buffer =3D kmalloc(bytes_recvd, GFP_ATOMIC);
> +			buffer =3D kmalloc(bytes_recvd, GFP_KERNEL);
>  			if (!buffer)
>  				return;
>  			continue;
> --
> 1.9.1