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Wed, 2 Jul 2025 11:17:27 +0000 Message-ID: <0ec290aa-0e9b-49cc-9dd7-2f58c51b6d22@intel.com> Date: Wed, 2 Jul 2025 19:17:18 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [BUG] Kernel panic in __migrate_swap_task() on 6.16-rc2 (NULL pointer dereference) To: "Aithal, Srikanth" , Jirka Hladky , Abhigyan ghosh CC: , Suneeth D References: <07D9F8BC-47A7-4E87-8655-C978C056E308@gmail.com> <31bd3395-cfe3-4af5-bc1c-fa8d26629b93@intel.com> <8a919ef6-4105-44e0-a17c-e41c1c0abbe9@amd.com> Content-Language: en-US From: "Chen, Yu C" In-Reply-To: <8a919ef6-4105-44e0-a17c-e41c1c0abbe9@amd.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: SG2PR02CA0028.apcprd02.prod.outlook.com (2603:1096:3:18::16) To DM4PR11MB6020.namprd11.prod.outlook.com (2603:10b6:8:61::19) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DM4PR11MB6020:EE_|MW4PR11MB5797:EE_ X-MS-Office365-Filtering-Correlation-Id: 5da481d0-143b-4325-c22f-08ddb95a06ad X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|1800799024|376014; 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>>>>                                            p->flags |= PF_EXITING >>>>                                         exit_mm >>>>                                            p->mm = NULL; >>>> >>>>     migrate_swap_stop >>>>       __migrate_swap_task((arg->src_task, arg->dst_cpu) >>>>        count_memcg_event_mm(p->mm, NUMA_TASK_SWAP)# p->mm is NULL >>>> >>>> Could you please help check if the following debug patch works, >>> >>> Attached the patch: >>> >>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c >>> index 8988d38d46a3..82fc966b390c 100644 >>> --- a/kernel/sched/core.c >>> +++ b/kernel/sched/core.c >>> @@ -3364,7 +3364,12 @@ static void __migrate_swap_task(struct >>> task_struct *p, int cpu) >>>   { >>>       __schedstat_inc(p->stats.numa_task_swapped); >>>       count_vm_numa_event(NUMA_TASK_SWAP); >>> -    count_memcg_event_mm(p->mm, NUMA_TASK_SWAP); >>> +    if (unlikely(!p->mm)) { >>> +        trace_printk("!! (%d %s) flags=%lx\n", p->pid, p->comm, >>> +                p->flags); >>> +    } else { >>> +        count_memcg_event_mm(p->mm, NUMA_TASK_SWAP); >>> +    } >>> >>>       if (task_on_rq_queued(p)) { >>>           struct rq *src_rq, *dst_rq; >> >> I was encountering the same issue as mentioned earlier in this thread, >> which has been recurring in our daily linux-next CI builds within our >> virtualization CI stream where we observed this BUG appearing randomly >> during the runs. >> >> Additionally, we were able to reproduce this issue while running the >> autonuma benchmark. As mentioned earlier, the BUG would occur randomly >> across iterations, typically between the 5th and 10th iterations. >> >> We consistently encountered this issue up to the 6.16.0-rc4- >> next-20250630 build [https://git.kernel.org/pub/scm/linux/kernel/git/ >> next/linux-next.git]. >> >> After applying the aforementioned patch ontop of next-20250630 build, >> I tested it in our virtualization CI and with the autonuma benchmark >> reproducer described below, and the issue no longer occurred. The >> patch appears to have resolved the reported problem. >> >> >> git clone https://github.com/pholasek/autonuma-benchmark.git >> cd autonuma-benchmark >> for i in $(seq 1 80); do bash ./start_bench.sh -s -t; done >> Note: The server running the autonuma-benchmark must have at least two >> nodes. >> >> If the provided fix is final, please feel free to include the >> following Tested-by tag: >> >> Tested-by: Srikanth Aithal >> Tested-by: Suneeth D >> > > > I apologize for overlooking that this was a debug patch. With this debug > patch applied on top of 6.16.0-rc4-next-20250630, I am unable to > reproduce the issue. However, when I revert this debug patch, I > encounter the issue again on 6.16.0-rc4-next-20250630. > > Thank you Aithal, this is a debug + fix patch. And Jirka has confirmed that this helps somehow. I'll post a formal one and Cc you. Thanks, Chenyu