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Mon, 11 May 2020 13:01:12 +0000 From: Damien Le Moal To: Alexander Potapenko , Bart Van Assche CC: Chaitanya Kulkarni , Jens Axboe , "linux-block@vger.kernel.org" , Willem de Bruijn , Dmitriy Vyukov Subject: Re: null_handle_cmd() doesn't initialize data when reading Thread-Topic: null_handle_cmd() doesn't initialize data when reading Thread-Index: AQHVm53GT+JHqNkf70+buklNLC0a/A== Date: Mon, 11 May 2020 13:01:12 +0000 Message-ID: References: <277579c9-9e33-89ea-bfcd-bc14a543726c@acm.org> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: google.com; dkim=none (message not signed) header.d=none;google.com; dmarc=none action=none header.from=wdc.com; x-originating-ip: [129.253.182.57] x-ms-publictraffictype: Email x-ms-office365-filtering-ht: Tenant x-ms-office365-filtering-correlation-id: 6d8d68d2-6832-401b-dc53-08d7f5ab619d x-ms-traffictypediagnostic: BY5SPR01MB0035: x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: wdcipoutbound: EOP-TRUE x-ms-oob-tlc-oobclassifiers: OLM:9508; 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x-ms-exchange-antispam-messagedata: 63zPEiGz9/W6ZQgOaxsyWvAzUWi51epMId2c08R5j/8wM0TkFfa/At6Ns4OZ5tZb/YXOjzd56Y0bap8WpI0lpcNP1QK4kb7Icebxi1PNX4LSBI6/ZPwvgyTMZjcJLD4VSQVrKFSz4n56ZV2Gl2AsTywX5TzFuhM45WgbchVCaqrQPAFM8X374Na78g4wNBrLB8ytM1t/QEXkDZvomjMh8NuZzDEuBZqyEtNPgiLk0EJw8fOXNFDwZbc6wxGX7iV0s/V+afzvI3BFVvcQppzdRZ2Nii82OUbXW9goyzxG+wLCynx/JbwnsEbl6SCLRgs6tYLP1Gu23Ow0Sm1VNf7XQSSzH2EjGrM1f8jKuPyAEEsl4ivJqy01Xqz8dOioYiy7DZ3uWq6UwNjd0H/8JZOghVc92lFQp914lLG6/1/720XcNwG1kZVPBoQ+Fv9XhlSqBesd471gfWT2YspJq1n1TXhIRQw/mLoM04IDVUixA1FFtJHKQvZu2OzXgHte8dEz Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: wdc.com X-MS-Exchange-CrossTenant-Network-Message-Id: 6d8d68d2-6832-401b-dc53-08d7f5ab619d X-MS-Exchange-CrossTenant-originalarrivaltime: 11 May 2020 13:01:12.0330 (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: BN74WuLMkFx4A9a1vjgV++JZ+DO1ZFsLxXbvRydGR8EyZdlXfjETRx47sgmD1eLtSVbeoG8rRB9ApJTnHCek9g== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BY5SPR01MB0035 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 2020/05/11 21:58, Alexander Potapenko wrote:=0A= > On Sun, May 10, 2020 at 6:20 PM Bart Van Assche wrot= e:=0A= >>=0A= >> On 2020-05-10 03:03, Alexander Potapenko wrote:=0A= >>> Thanks for the explanation!=0A= >>> The code has changed recently, and my patch does not apply anymore,=0A= >>> yet the problem still persists.=0A= >>> I ended up just calling null_handle_rq() at the end of=0A= >>> null_process_cmd(), but we probably need a cleaner fix.=0A= >>=0A= >> Does this (totally untested) patch help? copy_to_nullb() guarantees that= =0A= >> it will write some data to the pages that it allocates but does not=0A= >> guarantee yet that all data of the pages it allocates is initialized.=0A= > =0A= > No, this does not help. Apparently null_insert_page() is never called=0A= > in this scenario.=0A= > If I modify __page_cache_alloc() to allocate zero-initialized pages,=0A= > the reports go away.=0A= > This means there's no other uninitialized buffer that's copied to the=0A= > page cache, the nullb driver just forgets to write anything to the=0A= > page cache.=0A= =0A= Can you describe again the problem you are seeing please ? I can't find the= =0A= first email of this thread and forgot what the problem is.=0A= =0A= > =0A= >> diff --git a/drivers/block/null_blk_main.c b/drivers/block/null_blk_main= .c=0A= >> index 8efd8778e209..06f5761fccb6 100644=0A= >> --- a/drivers/block/null_blk_main.c=0A= >> +++ b/drivers/block/null_blk_main.c=0A= >> @@ -848,7 +848,7 @@ static struct nullb_page *null_insert_page(struct=0A= >> nullb *nullb,=0A= >>=0A= >> spin_unlock_irq(&nullb->lock);=0A= >>=0A= >> - t_page =3D null_alloc_page(GFP_NOIO);=0A= >> + t_page =3D null_alloc_page(GFP_NOIO | __GFP_ZERO);=0A= >> if (!t_page)=0A= >> goto out_lock;=0A= >>=0A= > =0A= > =0A= =0A= =0A= -- =0A= Damien Le Moal=0A= Western Digital Research=0A=