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Mon, 28 Jun 2021 04:36:24 +0000 From: Justin He To: Al Viro CC: Linus Torvalds , Petr Mladek , Steven Rostedt , Sergey Senozhatsky , Andy Shevchenko , Rasmus Villemoes , Jonathan Corbet , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , "Eric W . Biederman" , "Darrick J. Wong" , "Peter Zijlstra (Intel)" , Ira Weiny , Eric Biggers , "Ahmed S. Darwish" , "open list:DOCUMENTATION" , Linux Kernel Mailing List , linux-s390 , linux-fsdevel Subject: RE: [PATCH 13/14] d_path: prepend_path() is unlikely to return non-zero Thread-Topic: [PATCH 13/14] d_path: prepend_path() is unlikely to return non-zero Thread-Index: AQHXTEjX4vA9qb1/tUuDI9sxRSQuQasklodQgACoVwCAA7zVQIAAE8mAgAAF+mA= Date: Mon, 28 Jun 2021 04:36:24 +0000 Message-ID: References: <20210519004901.3829541-1-viro@zeniv.linux.org.uk> <20210519004901.3829541-13-viro@zeniv.linux.org.uk> In-Reply-To: Accept-Language: en-US, zh-CN Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ts-tracking-id: A4347E30F9F7144E9E154D3DFE84A780.0 x-checkrecipientchecked: true Authentication-Results-Original: zeniv.linux.org.uk; dkim=none (message not signed) header.d=none;zeniv.linux.org.uk; dmarc=none action=none header.from=arm.com; x-originating-ip: [203.126.0.112] x-ms-publictraffictype: Email X-MS-Office365-Filtering-Correlation-Id: 4ab2a488-970f-431e-ff6f-08d939ee5053 x-ms-traffictypediagnostic: AS8PR08MB5926:|AM6PR08MB5047: X-Microsoft-Antispam-PRVS: x-checkrecipientrouted: true nodisclaimer: true x-ms-oob-tlc-oobclassifiers: OLM:9508;OLM:9508; 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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-Transport-CrossTenantHeadersStamped: AS8PR08MB5926 Original-Authentication-Results: zeniv.linux.org.uk; dkim=none (message not signed) header.d=none;zeniv.linux.org.uk; dmarc=none action=none header.from=arm.com; X-EOPAttributedMessage: 0 X-MS-Exchange-Transport-CrossTenantHeadersStripped: VE1EUR03FT037.eop-EUR03.prod.protection.outlook.com X-MS-Office365-Filtering-Correlation-Id-Prvs: 3a966c50-2dfa-4847-47c4-08d939ee498c X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:63.35.35.123;CTRY:IE;LANG:en;SCL:1;SRV:;IPV:CAL;SFV:NSPM;H:64aa7808-outbound-1.mta.getcheckrecipient.com;PTR:ec2-63-35-35-123.eu-west-1.compute.amazonaws.com;CAT:NONE;SFS:(4636009)(136003)(396003)(39850400004)(346002)(376002)(36840700001)(46966006)(86362001)(186003)(966005)(81166007)(5660300002)(8676002)(83380400001)(7696005)(316002)(82740400003)(47076005)(36860700001)(2906002)(33656002)(70206006)(54906003)(53546011)(356005)(26005)(82310400003)(9686003)(478600001)(8936002)(450100002)(4326008)(70586007)(336012)(6862004)(52536014)(55016002)(6506007);DIR:OUT;SFP:1101; X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 28 Jun 2021 04:36:36.0008 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 4ab2a488-970f-431e-ff6f-08d939ee5053 X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[63.35.35.123];Helo=[64aa7808-outbound-1.mta.getcheckrecipient.com] X-MS-Exchange-CrossTenant-AuthSource: VE1EUR03FT037.eop-EUR03.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: AM6PR08MB5047 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Hi Al > -----Original Message----- > From: Al Viro On Behalf Of Al Viro > Sent: Monday, June 28, 2021 12:14 PM > To: Justin He > Cc: Linus Torvalds ; Petr Mladek > ; Steven Rostedt ; Sergey > Senozhatsky ; Andy Shevchenko > ; Rasmus Villemoes > ; Jonathan Corbet ; Heiko > Carstens ; Vasily Gorbik ; Christia= n > Borntraeger ; Eric W . Biederman > ; Darrick J. Wong ; Peter > Zijlstra (Intel) ; Ira Weiny ; > Eric Biggers ; Ahmed S. Darwish > ; open list:DOCUMENTATION doc@vger.kernel.org>; Linux Kernel Mailing List kernel@vger.kernel.org>; linux-s390 ; linux- > fsdevel > Subject: Re: [PATCH 13/14] d_path: prepend_path() is unlikely to return > non-zero > > On Mon, Jun 28, 2021 at 03:28:19AM +0000, Justin He wrote: > > > > On which loads? 1 here is "mount/dentry pair is in somebody > > > else's namespace or outside of the subtree we are chrooted > > > into". IOW, what's calling d_path() on your setup? > > > > No special loads, merely collecting the results after kernel boots up. > > > > To narrow down, I tested your branch [1] *without* my '%pD' series: > > [1] > https://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git/log/?h=3Dwor= k.d_ > path > > > > The result is the same after kernel boots up. > > IOW, you get 1 in call from d_absolute_path(). And the same commit has > - if (prepend_path(path, &root, &b) > 1) > + if (unlikely(prepend_path(path, &root, &b) > 1)) > there. What's the problem? > Ah, sorry for the mistake. -- Cheers, Justin (Jia He) > If you want to check mispredictions, put printks at the statements > under those if (unlikely(...)) and see how often do they trigger... IMPORTANT NOTICE: The contents of this email and any attachments are confid= ential and may also be privileged. If you are not the intended recipient, p= lease notify the sender immediately and do not disclose the contents to any= other person, use it for any purpose, or store or copy the information in = any medium. Thank you.