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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?QnVZZzRNYXZubmdsNit3aUZqMGlESStwdlZzTmh1UFZyNlVHN2FZUlVmY3dl?= =?utf-8?B?WG1tdGJkUk1lcHltVStlazJNaStoOU9KYzA3WlNPWjhjbmxyL25MSU5KKzhP?= =?utf-8?B?d1FmRGxMM2s3bU9WaGhjdFdGY3pDT0dhaER2b3lrakhtcFpXbVd3UTV5Snpj?= =?utf-8?B?T1VFNUxoeTl0Y3FHQm03Z1FzN2svMFlpeDF2WkRtbnRyaVlqd2tTSmhCN0pH?= =?utf-8?B?YmVMajJkK2NGWEo2QnZiaVA1VEV2Q04za1pBaGhNcnhUNGtOMkI2L0x6aW5H?= =?utf-8?B?UFNzd0JJenJPTXBoTjUyeGFYb1FDNjVPeG9RNlhqeTZPYWM3a055clZiQTJx?= =?utf-8?B?Q1dvNC9ldWdRVHl6eWt6cWtLMTRHQ1ZLOW1DUGdqYkYxSUt5S25adkZsSTRt?= =?utf-8?B?dHorU2tuQkZUemh0bUVHYkVXUERqZ0taN01mQjN4WDY0UkgzZnY5aDVQMS85?= =?utf-8?B?anFIbnRmL3J3VnZzdFJNcnpnOElEQmJZR3YxZzF3dDIwQ0tWb0VRVDZjdGtM?= =?utf-8?B?djNmTzRYVmMvUHFnYVZpcEJ1R1luQTdNeEpWWGZBM2VqRHZhOW43NkhXbnhZ?= =?utf-8?B?OCszak1ZSW9pUytiWU9KU1ZjekgrSUdqK1VsdktUNE5QRkdWcnV1Nk02cVJD?= =?utf-8?B?SmQyaCtqTEJGRnZCMlpRK1ZscmFwdFVPeEVzaHVqczZSQXBKL0g5dzlFYUpu?= =?utf-8?B?UHF5Y0kxREtyaUpjZWw4TWQ1aDJOVklTWDVjZ2RZYlc0cmViN2RveTVKMWlq?= =?utf-8?B?TExIYjh5elFQWUlrQkRYRGJzQ29jT0RodWJmNWs0T3cyYzMyZGM3T1lHL1h3?= =?utf-8?B?WHlRdEVmbHc4SU42V1VtdDRDSWFVeW5BTzRTWEZVYXBvV09IdVFrMjdHVmR1?= =?utf-8?B?bDZ4anRYWEQ5bU5jalBSSmppQkZyK3d6dDB0YTdiNFBORmtuRG5xMDJUMDdK?= =?utf-8?B?UGtSVTNRcUpDL1NacjZXblJzSXpqMXYvOG5CaVdBWHpPMzJpblhjWHJIYmg0?= =?utf-8?B?dTYyOE5CaFdXNTBuZGpRbnBZVnNKa1luSkR4Y254TG5UOFV5REYrbG5xSitX?= =?utf-8?B?NlpKWE1XR0ZYOVlTL0dPUUVJc2ZQODdoYzZKN2hHNXJXMy93U0Q2c0M1c2V2?= =?utf-8?B?aUd0Z0JaZkJCTGhyWm55NHZiYTZqTkFSeitNSjdMWkJEYXd4S3BKNmtvbC95?= =?utf-8?B?WEhlckxDcWt1MGYzUmJoKzAvWCtNNHNRRmVEMjYzRDVHM25mMHUrZGxsNGxs?= =?utf-8?B?NGgzQ21aSUJMY2wxSTVDRFhFRnBWVEFLSFkvOHNZYWZkNDRMWWE1ZUg5Zmdp?= =?utf-8?B?UHJrSWdwWUxpRC9kTUx2Q1BsSU5GZXpoaEpvak1CY09SVFgybC80QUxUMFVk?= =?utf-8?B?NGEzVnVxZWZhZGUvVm00bXRjQmZBOThDNHhaRi9na1FiMmhFam9wVFZGRE8z?= =?utf-8?B?ZHJUR1ZVeHI3YjBtaWJ2bzBvWHJNZ0FIY1VLWWZSN1VJVDJoL1J4V3V0QVA2?= =?utf-8?B?Sy92VUI0d0l6Q1lwVUVDVldRamJWUk9NOWJRQlk5WkNnVTJkdXBtZlkxc1o3?= =?utf-8?B?YmF2Q0g0UHhJZWpuQm9HSHNZRForbjdVSTNNZzFVczIveWcxeTN4WDNibHZu?= =?utf-8?B?eWNGVS9kSkxkSVNtWVRhQmZ1SHl3WlFPYVRqY1N2L2w5ekViVnJ6eENTSWho?= =?utf-8?B?M1VFdjJnRW82RzBVT0ljV1BKOWtuam5PY3NvcmZuVXArZk5HdmdJdmJpbDdk?= =?utf-8?B?S0kwNUZWaUo5TmhDVDQwWWZGakxwY2xQZzkrQVJQNVZxeC9BbUJLR0t6TEpQ?= =?utf-8?B?UElsTjdLVnA5SlVkRVQyTVBtTnBNWlJsV0tHVktxREN5bFVLNmN4Y1VNU2FJ?= =?utf-8?B?QkJtdndNcE04dzVyZkd3VVpWZzdMNHVyYkUzc1BNL1hJN1ZNeGlkUCtaKzA5?= =?utf-8?B?a2VPQnk4eU9LbXBCaTYxZXZsQmw5QTJkRGx6YVhVdWticEVLUjR6ZHppSEJ4?= =?utf-8?B?T0d1dGxIcDVvaW1HMDB1VDExcjhacVBaMlpqMUhxOG1oeWRwczVvNGxOV1dw?= =?utf-8?B?UjNJdUNlMmRWUWNscFJJL08vMVdCZUxmc0VsSWh4Sk5wOW5Mc2V4cGFhUytV?= =?utf-8?Q?Dy8RHtzY/oBJLottlIYN50Faz?= X-MS-Exchange-CrossTenant-Network-Message-Id: f3ae3342-feab-473f-03c5-08ddc5c35a2f X-MS-Exchange-CrossTenant-AuthSource: BYAPR11MB3320.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 18 Jul 2025 06:21:38.1970 (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: 6y/EnCzZ9nv9wE2JVHtNYfRawH7PAtko84CYzGk4HcVXJzdcbcu/R5+TXKPAu2CuVPN8bi+XbpfHkR3s3LuJ+Q== X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ5PPF2FCF00E1F X-OriginatorOrg: intel.com On 7/17/2025 12:21 PM, Sohil Mehta wrote: > On 7/17/2025 2:43 AM, Fushuai Wang wrote: >> The avx512_status() function would then dereference this >> NULL pointer via READ_ONCE(x86_task_fpu(task)->avx512_timestamp). >> when reading /proc/*/arch_status, causing a kernel NULL pointer dereference >> and system will crash. >> > > The kernel seems to assume that a Kthread would never call > x86_task_fpu(). That assumption is breaking in this scenario, which > causes the below issue. > This concern was discussed while adding the checks: https://lore.kernel.org/all/ZmFziN0i10sILaIo@gmail.com/ Adding a few folks who were involved in the discussion that time. > Can you please share any other warnings that were triggered before this > Oops message? Also, I'll try to generate this locally. Any specific > configuration needed for reproducing this apart from CONFIG_X86_DEBUG_FPU? > I was able to reproduce this on a system with X86_FEATURE_AVX512F. The issue only happens while reading arch_status on a kthread. $cat /proc/[kthread]/arch_status => NULL pointer exception $cat /proc/[user thread]/arch_status => No issue seen Can you confirm that you are seeing the same behavior? Unfortunately, avx512_timestamp resides within struct fpu. So getting that value for a kthread would mean going through x86_task_fpu(). I am wondering if we ever need to expose the AVX512 usage for kernel threads? If not, then we can do what you currently have but without the CONFIG_X86_DEBUG_FPU restriction. All kernel threads would always print the AVX512_elapsed_ms as -1. However, this would be a user visible change so we should probably get more inputs. I tried this experiment on an older kernel without the above issue. Among all the active kthreads on my system a handful of them show a valid value for AVX512 usage. The rest of them all show -1. PID: 2594 CMD: avahi-daemon: running [SAP.local] /proc/2594/arch_status content: AVX512_elapsed_ms: 46032 PID: 2729 CMD: sshd: /usr/sbin/sshd -D [listener] 0 of 10-100 startups /proc/2729/arch_status content: AVX512_elapsed_ms: 396656 To keep the older behavior, we might need to consider moving avx512_timestamp out of struct fpu. Though, I am uncertain about its implication. >> >> diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c >> index 9aa9ac8399ae..16f813a42f42 100644 >> --- a/arch/x86/kernel/fpu/xstate.c >> +++ b/arch/x86/kernel/fpu/xstate.c >> @@ -1859,9 +1859,14 @@ long fpu_xstate_prctl(int option, unsigned long arg2) >> */ >> static void avx512_status(struct seq_file *m, struct task_struct *task) >> { >> - unsigned long timestamp = READ_ONCE(x86_task_fpu(task)->avx512_timestamp); >> + unsigned long timestamp = 0; >> long delta; >> >> +#ifdef CONFIG_X86_DEBUG_FPU >> + if (!(task->flags & PF_KTHREAD)) >> +#endif > > The logical code flow should not change based on X86_DEBUG_FPU. The fix > for this issue likely needs to be somewhere else. Though, I am still > working on identifying the exact root cause. > >> + timestamp = READ_ONCE(x86_task_fpu(task)->avx512_timestamp); >> + >> if (!timestamp) { >> /* >> * Report -1 if no AVX512 usage >