Subject: Re: [PATCH] nfs: block notification on fs with its own ->lock
To:     "J. Bruce Fields" <bfields@fieldses.org>,
        Chuck Lever <chuck.lever@oracle.com>
Cc:     linux-nfs@vger.kernel.org, Jeff Layton <jlayton@kernel.org>,
        "Denis V. Lunev" <den@virtuozzo.com>,
        Cyrill Gorcunov <gorcunov@virtuozzo.com>,
        Konstantin Khorenko <khorenko@virtuozzo.com>
References: <20211216172013.GA13418@fieldses.org>
From:   Vasily Averin <vvs@virtuozzo.com>
Message-ID: <bb7b5a71-6ddf-5e22-e555-8ae22e5930fe@virtuozzo.com>
Date:   Fri, 17 Dec 2021 09:41:03 +0300
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101
 Thunderbird/78.14.0
In-Reply-To: <20211216172013.GA13418@fieldses.org>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?c2tJdHlMR3dmWUN0NFl5b2xHb0pNTE9tcXJQUHAvV1dBSlc0L3pxNWllTWlo?=
 =?utf-8?B?eldobzM0eVdyMDZxT0dCV1dDcDNOanp0MzNRR1NsckJ5VlllZUJwQnQyTFg0?=
 =?utf-8?B?dTN2Z1ZlUmtDNTdROEg4SG5NSGlhZ2RLVEJpaGtQYWZJbzhHTW16SU1oTDg3?=
 =?utf-8?B?ZC9TZDA4aURpYWw1MjZhQWhpSHpzK0ZsTmhvc0VzTm9uQXRUd29ZRExIMG14?=
 =?utf-8?B?cXNKbTVHeWJnZHhWL1lNYkkzNWR3VE1BSVVRMzc0TG42ZlZOYStWY2lKa3pP?=
 =?utf-8?B?M2czRWk4aDkvZ1VYRXVWZytVdFRZRzVhaDA3cEgvQTdhN3c0S0pqby9aeEI3?=
 =?utf-8?B?bHZGcVBNSFNzMkJrTzVERmwyakNtZldSWENSSG44emJabVVJWS9FRHlVNFZp?=
 =?utf-8?B?ODJBYVB2ZTlzaktYaU93U0FHYzhSUlBXenpPVDlqU29vYVFwc2RSY2RKd011?=
 =?utf-8?B?M3NrZFp3SHVPZ043VnNIaW5tYVNUank1RWFCaWh3UWZxMTIwZG96eUs1RVhx?=
 =?utf-8?B?NUkrQVBGVVZiZUdabjNXVHBUMkg0MzMwNEt0TnJFRG41NGpTTXhJQzZnOHZn?=
 =?utf-8?B?dVV3TE84eGczdEVxTkJKSjJtbDRtSkpXME9JWmp4SHVuSlhZcXBSNllvWkh3?=
 =?utf-8?B?Q3VEaHpTWmlXSm9VL3hQQXI4TDJZcmlTZkk2TjlwMlkraVRYVGZoclJ0N0F1?=
 =?utf-8?B?TXhVUDFSdFJXOENKVTk5UjBoN1BNZ3FIdkJaOC9FeVk0QVp5elAzQkdFVEdr?=
 =?utf-8?B?ZDBnUitKOFQxWnNsS280ZFdmM2dJWVo2eWZtUmRXdGZmWDR6Tm4rZnI5SDRj?=
 =?utf-8?B?Vi81aUhDTmk2UXBOS24wZE5vd21yS1U3SHAwTnpPaVJHNm1UN0lwUWczVi9s?=
 =?utf-8?B?QXRLY0tWYXk4NzZoK29aRW81Y01FbzNjckNmRkdKRWs4Ykc3NS85L1BlY1l2?=
 =?utf-8?B?MXpZanh3M3A0RysxS3FvbG9OeXZZZ2I5Q1oweWJGWFNzd0NiOUJ5SWdvS3Rh?=
 =?utf-8?B?aFV4Y2xvZWRPN1A4Q2YzUkttZ28rUUZKSVJYSnE5LzhzTUhBSUV6Y0Zkd1FQ?=
 =?utf-8?B?Z3BXRS9sV1R1bWNVRDlOb3RSSnFYUFJvbzNETThBVHFDcm01dW1sWktaQWFz?=
 =?utf-8?B?S25LaTZlV09ZelVMcUJzc01mN1hZV3B3eG1SajE5d24yaTgwbFNVUGpGcjVx?=
 =?utf-8?B?NjBnMGZnNXlBdVVFMXNwazhFZ3I5bHdpb3lNTHI5STF3MDgvVmRXOHF3VXlj?=
 =?utf-8?B?bGl4WTY1MjNjZUhSZFdDeHhQbWtiN2lJYWF6VFRja3QxVWs5RUpURk1mdDBp?=
 =?utf-8?B?SkMzVjFPaXZSS080UklFQitBRFMwK01Hc05PSjgyeVI3Q0dpMHcxelRQWnFG?=
 =?utf-8?B?OERRQzRaaTk4ZkNnV3VNQ0c2enRkbUErUG0vTmt1RVN6aUh6SEdKSU00VzVq?=
 =?utf-8?B?bGt5R2ljMFRReGNkOXVCSzJIMi82cjBQdGJFTm1aQ0pjaENGUzl4bzUyRDRP?=
 =?utf-8?B?SnZhSFZtdlkzekxzRjFVUlJWQnZvZWhwdmg4bVJsc0pNcy9meTVYNnQ5ZTRr?=
 =?utf-8?B?S3BrYXNkdVBDeWpEeUV6TlFiVS9FV2x1ZnpJZG9QVXVYdjJDRWNRNjNCSk41?=
 =?utf-8?B?M3N6YjIrNC9PcHZpRlVya012SzZ1SVdhUUhRRWtnaGtKc3hjQS9CdkFTdW9B?=
 =?utf-8?B?aGNrM3dkWjd1SWhGUHJjY09tQ0ZtN3ZCSjRDVWQvbjJBT0UxRnVydWV3YjR2?=
 =?utf-8?B?M0ZzQ0VjVXdNSmNYamw2VXArenlUcnRERVlTaXZXSjBGc3dJdjFINlVvY01z?=
 =?utf-8?B?aVgyVldDOTlTWHRCWStPRURyajVHRDc2OVZ1LzMzY3lqc3pXU3F3QU1iNjdC?=
 =?utf-8?B?UG1udG1TWWxvQTZyd3M3LzVIc1U1aXg2R0ZwdGs5Y2c3Qmk2cFhUQm14MTlx?=
 =?utf-8?B?RVVKQmFna3k3cE9GWkZOZTlFek5NVzRETHJmZWtXME81czFzTkN5N0p0T1FL?=
 =?utf-8?B?djBoOWM1Z0dkbGg5bzhyWjVtbWtwWkJwRjJKV3g2d1EwRnUzR0Y4S3NEcHMy?=
 =?utf-8?B?VmV5ci93ZkprcnBQd0w3T1E1QjZ0Z2hIWkdxQXRubkZFOXNrOGg5QTlpd2l2?=
 =?utf-8?B?SlpZWWhjNm51L243ZnhKTDJxK2NJYk9QN0ZpNXl4SWt3L0pSV2cyTjVqQWM2?=
 =?utf-8?Q?JRRmFA4VsieT5JDemHnXCfM=3D?=
X-OriginatorOrg: virtuozzo.com
X-MS-Exchange-CrossTenant-Network-Message-Id: 25c5cbf0-d9c2-4557-6254-08d9c1283305
X-MS-Exchange-CrossTenant-AuthSource: DB9PR08MB6619.eurprd08.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 17 Dec 2021 06:41:05.1964
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 0bc7f26d-0264-416e-a6fc-8352af79c58f
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: T8r6DJpsQw5In+YeV17PtBTeGcPV3zYU4ZBjZu8Gc4dIUPYxxqjAsbL7lCOiH2jqayulZeSN9ktKi9xr+nBNHw==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: DBBPR08MB4727
Precedence: bulk
List-ID: <linux-nfs.vger.kernel.org>
X-Mailing-List: linux-nfs@vger.kernel.org

On 16.12.2021 20:20, J. Bruce Fields wrote:
> From: "J. Bruce Fields" <bfields@redhat.com>
> 
> NFSv4.1 supports an optional lock notification feature which notifies
> the client when a lock comes available.  (Normally NFSv4 clients just
> poll for locks if necessary.)  To make that work, we need to request a
> blocking lock from the filesystem.
> 
> We turned that off for NFS in f657f8eef3ff "nfs: don't atempt blocking
> locks on nfs reexports" because it actually blocks the nfsd thread while
> waiting for the lock.
> 
> Thanks to Vasily Averin for pointing out that NFS isn't the only
> filesystem with that problem.
> 
> Any filesystem that leaves ->lock NULL will use posix_lock_file(), which
> does the right thing.  Simplest is just to assume that any filesystem
> that defines its own ->lock is not safe to request a blocking lock from.
> 
> So, this patch mostly reverts f657f8eef3ff and b840be2f00c0, and instead
> uses a check of ->lock (Vasily's suggestion) to decide whether to
> support blocking lock notifications on a given filesystem.  Also add a
> little documentation.
> 
> Perhaps someday we could add back an export flag later to allow
> filesystems with "good" ->lock methods to support blocking lock
> notifications.
> 
> Reported-by: Vasily Averin <vvs@virtuozzo.com>
> Signed-off-by: J. Bruce Fields <bfields@redhat.com>

Reviewed-by: Vasily  Averin <vvs@virtuozzo.com>