Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Mon, 7 Nov 2022 12:26:21 -0400
From:   Jason Gunthorpe <jgg@nvidia.com>
To:     Qi Zheng <zhengqi.arch@bytedance.com>
Cc:     dvyukov@google.com, willy@infradead.org, akinobu.mita@gmail.com,
        akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
        stable@vger.kernel.org
Subject: Re: [PATCH] mm: fix unexpected changes to
 {failslab|fail_page_alloc}.attr
Message-ID: <Y2kxrerISWIxQsFO@nvidia.com>
References: <CACT4Y+Zc21Aj+5KjeTEsvOysJGHRYDSKgu_+_xN1LUYfG_H0sg@mail.gmail.com>
 <20221107033109.59709-1-zhengqi.arch@bytedance.com>
 <Y2j9Q/yMmqgPPUoO@nvidia.com>
 <4736d199-7e70-6bc3-30e6-0f644c81a10c@bytedance.com>
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <4736d199-7e70-6bc3-30e6-0f644c81a10c@bytedance.com>
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?8WVuukeEm6Vr3LX4BbHDFKGkdy6N884S9hbC8q2ZgawxNNa+6ZmbgAvDSi4i?=
 =?us-ascii?Q?lj9CpwaLmNpgbCgXAibQMzQXwO8s9fflc37l2/qnDXyaaqjj3SlMNfV1sSiF?=
 =?us-ascii?Q?/HwZ/MeR9VcS0Uc9M/isG0BcYq3OfEA9Ga3M6qgp4SRBCV4uez1BHaoa6EEM?=
 =?us-ascii?Q?Y7q7hk8l0b9atIh8rZ6ZpWUIHNiudYAu+w5LC74ERGaMm+B9uR5KgLWLtP0W?=
 =?us-ascii?Q?T6eJ6om8uZjXVsL0ZO/kbs8S/lnekwgOOjBMfjCTcT5UVb3pLswNOx4aUmMq?=
 =?us-ascii?Q?78yWUKRK1aGAsHOVIozL5Rr5JHGdYIOWBd8h09DEOFXvbEdxYUuzVHZKvJas?=
 =?us-ascii?Q?oVLCU81/broOY4YqVHW461eVZnKDvOE0sao/t4yyRUQ5GHpD+nviJQw/wYmx?=
 =?us-ascii?Q?9zusVIKGL8lCwZUmwpIiwss0fRg2F98rCoK77cI+tWPiSzHgMvthLjmJJC+x?=
 =?us-ascii?Q?qudfh55BKZuZHplsMnxPpwEduHCtikU0tgcWX+UB32GBpg2ROhRkwTB7gDxP?=
 =?us-ascii?Q?ig2oUj37hXrczcdTpQtPG3S73CaOYIzM5KnfGp0fxiUhmpShFS+H/QyUGhsE?=
 =?us-ascii?Q?eFo+SXYYm4DCKniwbSnZMlyKPTJKCSburH7NrIJyEKLeC5PLyHpyuLOew47z?=
 =?us-ascii?Q?wrWsXCc5nOg9CpEksbc2uoPQW7pZwfy5RBqUl4DYvzI7RI32+otCmTaI0oPt?=
 =?us-ascii?Q?rPYjMAFSAIt18yXGtJsDZKD9wGlgfYtcD5+wQDBvYUnbgcmVMOVe4sOuBj5F?=
 =?us-ascii?Q?K9dn7a1M5KOJTWAAyyctcfwbgdqAWfsT+ro6xwA/A6ZAQxZG59SmFJbk28Cn?=
 =?us-ascii?Q?xP983MTtkHiDPXZ/NhOzFAlScWykp6QvY230LgIi2wt6UE19pWzI6AYz99TM?=
 =?us-ascii?Q?iGOD+4i6vH1DFkXP06ePxSE9zjsFHT/kFH27DykQvZuMConv2xFfJJtnE6sW?=
 =?us-ascii?Q?Sx+4LM5mlVMRm+pY5jfxcb6sHMky9njkAV7WQysdHbqnqtspL1eV9eK1cySJ?=
 =?us-ascii?Q?/f/Rt6LRbN0lR3gxTf8Nj/NKqjefbSggRTrMTn9Vi8/ma3ezdPFDbm8Dk6td?=
 =?us-ascii?Q?uSLHibIAlIOxMJfvM0WtEl5V59YCAI+tpY5Vz5NH1gsuDiG04jArbGrSabEU?=
 =?us-ascii?Q?Glt+Lu0OR4C9GBVj6fuXdryDjhGzjVVNPoPbg2Tgy8pRoV88HHBMgV8Dixk5?=
 =?us-ascii?Q?B1gnZRLiTXvLZC9DLf/+YdmXZzTJbSi+7t3WiRMCs+VvVE7+MAEoDbWj72z4?=
 =?us-ascii?Q?SPku336HRd/bNKpGNV3ElzFYCn8PNeFOO1+KCxeJGCWNFwkrv8fhDzgNvIkL?=
 =?us-ascii?Q?/Fj3wpg+vDKEbeoD3jjhaCz7y/8fSsvaoRnxeacOK4Uy4RmHihFGIzmiQgjV?=
 =?us-ascii?Q?yNoQzEqvB3WfBgK0nCKdGPLQDYnizYDjdVn2WpfeKeY/adzirKtYwDpGURzF?=
 =?us-ascii?Q?HGWkDSzyPL/6XjRt/9txlSC7fdRUHeCBTvcbxNIH/Kzrn/pZnZhWvC0escNo?=
 =?us-ascii?Q?q0eS0ZS84Lm9fDbbVymtidWInw0zJQHkgy2YLMGyDCwEZqoMzC/C4NtjTOGB?=
 =?us-ascii?Q?VC5EhptfJykNmvuQkcw=3D?=
X-OriginatorOrg: Nvidia.com
X-MS-Exchange-CrossTenant-Network-Message-Id: 7aa3efc5-5a27-4357-9579-08dac0dccec0
X-MS-Exchange-CrossTenant-AuthSource: LV2PR12MB5869.namprd12.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 07 Nov 2022 16:26:22.1348
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: CFmf2C+O4Of7ui2rzqR1QLMsoR+VH3A6MWEMBOrBL99pkeamSoabEfYLtJRZ8IXg
X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW4PR12MB5626
X-Spam-Status: No, score=-1.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,
        DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FORGED_SPF_HELO,
        RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_PASS,SPF_NONE
        autolearn=no autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Mon, Nov 07, 2022 at 11:05:42PM +0800, Qi Zheng wrote:
> 
> 
> On 2022/11/7 20:42, Jason Gunthorpe wrote:
> > On Mon, Nov 07, 2022 at 11:31:09AM +0800, Qi Zheng wrote:
> > 
> > > @@ -31,9 +33,9 @@ bool __should_failslab(struct kmem_cache *s, gfp_t gfpflags)
> > >   		return false;
> > >   	if (gfpflags & __GFP_NOWARN)
> > > -		failslab.attr.no_warn = true;
> > > +		flags |= FAULT_NOWARN;
> > 
> > You should add a comment here about why this is required, to avoid
> > deadlocking printk
> 
> I think this comment should be placed where __GFP_NOWARN is specified
> instead of here. What do you think? :)

NOWARN is clear what it does, it is this specifically that is very
subtle about avoiding deadlock aginst allocations triggered by
printk/etc code.

Jason