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b=xrXUETFdRDPgSSzdfBFDKPzBiQFoNf61PryAop4+WrplDY5A5bA02xA++R/nVL/mxVrx+X0Q10yuHhdy66ITTCvo1Wbb4VT5RWJ5uNasE9UWQi/ikSdwETeSq+02PAV5AeRKTUw+Yp4CC7fpYqZdfOLPQSfje4oggoH4O1WUm9c= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=amd.com; Received: from IA1PR12MB6460.namprd12.prod.outlook.com (2603:10b6:208:3a8::13) by BL3PR12MB6377.namprd12.prod.outlook.com (2603:10b6:208:3b0::15) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8880.28; Wed, 2 Jul 2025 12:19:19 +0000 Received: from IA1PR12MB6460.namprd12.prod.outlook.com ([fe80::c819:8fc0:6563:aadf]) by IA1PR12MB6460.namprd12.prod.outlook.com ([fe80::c819:8fc0:6563:aadf%6]) with mapi id 15.20.8901.018; Wed, 2 Jul 2025 12:19:18 +0000 Message-ID: <5bcb752d-813e-4ab4-8519-fae897472b5b@amd.com> Date: Wed, 2 Jul 2025 17:49:13 +0530 User-Agent: Mozilla Thunderbird Subject: Re: [BUG] Kernel panic in __migrate_swap_task() on 6.16-rc2 (NULL pointer dereference) To: Jirka Hladky , "Chen, Yu C" Cc: Abhigyan ghosh , linux-kernel@vger.kernel.org, Suneeth D References: <07D9F8BC-47A7-4E87-8655-C978C056E308@gmail.com> <31bd3395-cfe3-4af5-bc1c-fa8d26629b93@intel.com> <8a919ef6-4105-44e0-a17c-e41c1c0abbe9@amd.com> <0ec290aa-0e9b-49cc-9dd7-2f58c51b6d22@intel.com> Content-Language: en-US From: "Aithal, Srikanth" In-Reply-To: Content-Type: text/plain; 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Entries in Buffer/Entries Written: 0/0 > On Wed, Jul 2, 2025 at 1:17 PM Chen, Yu C wrote: >> >> On 7/2/2025 3:36 PM, Aithal, Srikanth wrote: >>> >>> >>> On 7/2/2025 10:02 AM, Aithal, Srikanth wrote: >>>> On 6/27/2025 1:03 PM, Chen, Yu C wrote: >>>>> On 6/27/2025 3:16 PM, Chen, Yu C wrote: >>>>>> Hi Jirka, >>>>>> >>>>>> On 6/27/2025 5:46 AM, Jirka Hladky wrote: >>>>>>> Hi Chen and all, >>>>>>> >>>>>>> we have now verified that the following commit causes a kernel panic >>>>>>> discussed in this thread: >>>>>>> >>>>>>> ad6b26b6a0a79 sched/numa: add statistics of numa balance task >>>>>>> >>>>>>> Reverting this commit fixes the issue. >>>>>>> >>>>>>> I'm happy to help debug this further or test a proposed fix. >>>>>>> >>>>>> >>>>>> Thanks very much for your report, it seems that there is a >>>>>> race condition that when the swap task candidate was chosen, >>>>>> but its mm_struct get released due to task exit, then later >>>>>> when doing the task swaping, the p->mm is NULL which caused >>>>>> the problem: >>>>>> >>>>>> CPU0 CPU1 >>>>>> : >>>>>> ... >>>>>> task_numa_migrate >>>>>> task_numa_find_cpu >>>>>> task_numa_compare >>>>>> # a normal task p is chosen >>>>>> env->best_task = p >>>>>> >>>>>> # p exit: >>>>>> exit_signals(p); >>>>>> 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 >> > >