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Wong" , Bagas Sanjaya , , , , , , Linux Regressions Subject: Re: [Syzkaller & bisect] There is BUG: unable to handle kernel NULL pointer dereference in xfs_extent_free_diff_items in v6.4-rc3 Message-ID: References: <20230522160525.GB11620@frogsfrogsfrogs> <20230523000029.GB3187780@google.com> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: X-ClientProxiedBy: SGBP274CA0022.SGPP274.PROD.OUTLOOK.COM (2603:1096:4:b0::34) To PH0PR11MB4839.namprd11.prod.outlook.com (2603:10b6:510:42::18) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH0PR11MB4839:EE_|SN7PR11MB6948:EE_ X-MS-Office365-Filtering-Correlation-Id: 0f52fc98-f5eb-46f2-4931-08db5bfd2f72 X-LD-Processed: 46c98d88-e344-4ed4-8496-4ed7712e255d,ExtAddr X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:PH0PR11MB4839.namprd11.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230028)(346002)(366004)(396003)(136003)(376002)(39860400002)(451199021)(66556008)(5660300002)(8936002)(8676002)(44832011)(83380400001)(86362001)(6512007)(53546011)(6506007)(26005)(186003)(82960400001)(38100700002)(4326008)(478600001)(6486002)(6916009)(316002)(41300700001)(54906003)(2906002)(66476007)(66946007)(67856001);DIR:OUT;SFP:1102; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?vJxh+TIdCG8zi44sHTksfsi3LUgIWztlyOhOL14+posLs/YJHkGDeDOD6FdL?= =?us-ascii?Q?1BcbNRpe6JS6fbRl9ChJJ3PfNFjWMaHYA9niMJmCYIgT6/0PAImztaOiYihF?= =?us-ascii?Q?A2NMbG64fssOeMJbOGDldzSvQs7XRV8pAPeHG7BmgWGixbd74kFQ+t1e0kcj?= =?us-ascii?Q?US6GevM0thJ59gcgQST4QcitRx/yWs/eby0dZ5ZMzvYZdd09xZiykSIaj3lK?= =?us-ascii?Q?ilgOPVqmqv8DnanhxqZ+StCMSSwoMW6wErL+nyr+tK+hfFvvbJpe0QBMClAp?= =?us-ascii?Q?jFR6NnRtxzoXmEsiKQKiEgvACxmAi0mNSEqpADDZOt6w04bkZVJDl2MDfxGe?= =?us-ascii?Q?Cr920pSoYygXK4EKqc3UFSMJW1JBjsxd1ySyd+u8J40v10eZviiSWtXH928P?= =?us-ascii?Q?sVEoitHGZQCyROGEr51iVPWQt0IxPjDopLQShXJscVuEDSIqTvRG178L/G6w?= =?us-ascii?Q?9e63SpLmahymUSS1Wolod46vbvXpFp3SEoOqGEoseDgWxi1BvA8BfN3Npgm1?= =?us-ascii?Q?Iyphx1cHn7Xz2UaOyR5w2pYqx9Peqlfbd/f6zJqCKN9WwozZLF/n/k8JRoLY?= =?us-ascii?Q?y82rrcF3FmRVZi98FevVJCWdceXcflgbl8sC3D2AMZXGYWxh+CIWxGUaeGG8?= =?us-ascii?Q?5QeNc/lLNR/Y5aLJth87xiPDV/Qe2EPzti1+rgWVq9rDAzvxB7LSf83gB55P?= =?us-ascii?Q?dIXPAJ8JliCmsY1kXAnyuKwKQTqJh5hK6MgRxKt0BqpK3mEY8XCLLP1Ybp5d?= =?us-ascii?Q?3xmxJ3b0C04tASGt924IgN9ZfN8lLOKknXUkUCbhVB8CCtfA4B782KSzFZaa?= =?us-ascii?Q?oNVGeecfmfVDCQFIlFf9TKjK25ug+9RWHdISWHKIzBpQoO6yXW/u4vY+pk20?= =?us-ascii?Q?MU79VLceYHuEd/y0rvshigZ3A0apbLg6Ym/VVznJdj+TmcpCLg/yyQE/0bZg?= =?us-ascii?Q?np8XURT17SiH53Yeadlt1gAToq4z1aqlYhI4+UwAG2kUum9NFt2r964WrLa0?= =?us-ascii?Q?+zPiEXw9cRA76E1Lv3y/NhqzNB2taqwLrWFTDpSKsXla6f4XH0Sg9pIMpw60?= =?us-ascii?Q?JuehexWMbuYmnoPLuXN+Boou6ZpcZd6lA8QIHvRTzNDX3jnP92X0Y6rh6/NQ?= =?us-ascii?Q?EE5GBNCHU5gkNtmage183uSBlX/7r3GOrF97VsEQRVnfMbyTiAD8irEnEgLE?= =?us-ascii?Q?caw2K/Vuh36Fj1ZHT556X/4ZdKmF0VLsCx8k3ErSMF6g0DF30woXg7oeTAL1?= =?us-ascii?Q?+HbvcH/cUMsxWbGDSGcWECgIZJIO7B4Q0PCV9xo6s1SPP6IooEnht49wjcIm?= =?us-ascii?Q?QHnqxBSAwz9iGKrXDN5JMsxN+2/vecW2INBqNtue8m9uufFhAAnZUwY+cwVq?= =?us-ascii?Q?vkXJrNFgWfmpHaU7PXNUu6l+UmZkrweqooUJC+uRMOxtiHZteNdGQcdvw0IW?= =?us-ascii?Q?oLiFkR1cTgZ9Ajg9iz6pyR9j93gU6Hz079iSceR1Qy8jWgAhw8DW2zlDkjoE?= =?us-ascii?Q?k/TaknS0cHFdP/y4HXmnQLDhPBl3LU21VPewtjkQyl1P7wxGdRIBZcLhJIcC?= =?us-ascii?Q?bf5yv1VGStWAEBGZwhCM1p9Jfgxh9r5Kn2aOkGYP?= X-MS-Exchange-CrossTenant-Network-Message-Id: 0f52fc98-f5eb-46f2-4931-08db5bfd2f72 X-MS-Exchange-CrossTenant-AuthSource: PH0PR11MB4839.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 24 May 2023 02:18:38.6658 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: Qwi0zOfsyVY9VTqHKgPHU0RmMDgHl/zjpB5tl2mlDr7wsPAVCsHa9fLtupS82h0i7ULB2J2ZgE8JrohFASMKpA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN7PR11MB6948 X-OriginatorOrg: intel.com Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On 2023-05-24 at 07:52:59 +1000, Dave Chinner wrote: > On Tue, May 23, 2023 at 05:14:24PM +0800, Pengfei Xu wrote: > > I did not do well in two points, which led to the problem of this useless > > bisect info: > > 1. Should double check "V4 Filesystem" related issue carefully, and should > > give reason of problem. > > 2. Double check the bisect bad and good dmesg info, this time actually > > "good(actually not good)" dmesg also contains "BUG" related > > dmesg, but it doesn't contain the keyword "xfs_extent_free_diff_items" > > dmesg info, and give the wrong bisect info. > > Sorry for inconvenience... > > I think you misunderstand. > > The bisect you did was correct - the commit it > identified was certainly does expose the underlying issue. > > The reason the bisect, while correct, is actually useless is that it > the underlying issue that the commit tripped over is not caused by > the change in the commit. The underlying issue has been there for a > long while - probably a decade - and it's that old, underlying issue > that has caused the new code to fail. > > IOWs, the problem is not the new code (i.e. it is not a regression > in the new code identified by the bisect), the problem is in other > code that has been silently propagating undetected corruption for > years. Hence the bisect is not actually useful in diagnosing the > root cause of the problem. > Thanks a lot Dave's description! It's clear. Anyway I will remove "CONFIG_XFS_SUPPORT_V4" in syzkaller fuzzing test next time to avoid the noise. Thanks also to Eric Biggers, Bagas Sanjaya and all community's help! Thanks! BR. > Cheers, > > Dave. > -- > Dave Chinner > david@fromorbit.com