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Tue, 4 Aug 2020 14:39:57 +0000 From: Johannes Thumshirn To: Coly Li , "linux-block@vger.kernel.org" CC: "linux-bcache@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Ming Lei , Hannes Reinecke , Xiao Ni , Bart Van Assche , Christoph Hellwig , Enzo Matsumiya , Jens Axboe , Evan Green Subject: Re: [PATCH] block: tolerate 0 byte discard_granularity in __blkdev_issue_discard() Thread-Topic: [PATCH] block: tolerate 0 byte discard_granularity in __blkdev_issue_discard() Thread-Index: AQHWamrhOskbhhn9f0O9q4CKi9C/MA== Date: Tue, 4 Aug 2020 14:39:56 +0000 Message-ID: References: <20200804142332.29961-1-colyli@suse.de> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: suse.de; dkim=none (message not signed) header.d=none;suse.de; dmarc=none action=none header.from=wdc.com; x-originating-ip: [129.253.240.72] x-ms-publictraffictype: Email x-ms-office365-filtering-ht: Tenant x-ms-office365-filtering-correlation-id: 9febf1dc-02be-4aca-a42f-08d83884422e x-ms-traffictypediagnostic: SN6PR04MB4317: x-microsoft-antispam-prvs: wdcipoutbound: EOP-TRUE x-ms-oob-tlc-oobclassifiers: OLM:8882; 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charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: wdc.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: SN4PR0401MB3598.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 9febf1dc-02be-4aca-a42f-08d83884422e X-MS-Exchange-CrossTenant-originalarrivaltime: 04 Aug 2020 14:39:56.8987 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: b61c8803-16f3-4c35-9b17-6f65f441df86 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: LDMw2OUG3dRA3e7UzNzq+SoOeze1lICK9vz2EAub4yFBagesN8yFrnF3TgUKTC3k6UKD20c7U2IAreNqADJFZPRIRpdoiPoR2l4muxifARE= X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN6PR04MB4317 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 04/08/2020 16:37, Johannes Thumshirn wrote:=0A= > On 04/08/2020 16:34, Coly Li wrote:=0A= >> On 2020/8/4 22:31, Johannes Thumshirn wrote:=0A= >>> On 04/08/2020 16:23, Coly Li wrote:=0A= >>>> This is the procedure to reproduce the panic,=0A= >>>> # modprobe scsi_debug delay=3D0 dev_size_mb=3D2048 max_queue=3D1=0A= >>>> # losetup -f /dev/nvme0n1 --direct-io=3Don=0A= >>>> # blkdiscard /dev/loop0 -o 0 -l 0x200=0A= >>>=0A= >>> losetup -f /dev/sdX isn't it?=0A= >>>=0A= >>=0A= >> In my case, I use a NVMe SSD as the backing device of the loop device.= =0A= >> Because I don't have a scsi lun.=0A= >>=0A= >> And loading scsi_debug module seems necessary, otherwise the discard=0A= >> process just hang and I cannot see the kernel panic (I don't know why ye= t).=0A= > =0A= > OK, now that's highly interesting. Does it also happen if you back loop w= ith=0A= > a file? loop_config_discard() has different cases for the different backi= ng devices/files. S=0A= > =0A= =0A= Damn I didn't want to hit sent....=0A= =0A= Does this (untested) change make a difference:=0A= =0A= diff --git a/drivers/block/loop.c b/drivers/block/loop.c=0A= index 475e1a738560..8a07a89d702e 100644=0A= --- a/drivers/block/loop.c=0A= +++ b/drivers/block/loop.c=0A= @@ -895,6 +895,9 @@ static void loop_config_discard(struct loop_device *lo)= =0A= blk_queue_max_write_zeroes_sectors(q,=0A= backingq->limits.max_write_zeroes_sectors);=0A= =0A= + q->limits.discard_granularity =3D=0A= + backingq->limits.discard_granularity;=0A= +=0A= /*=0A= * We use punch hole to reclaim the free space used by the=0A= * image a.k.a. discard. However we do not support discard if=0A= =0A=