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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?N3Vac3FzSFNSRG5reDBPYjdCbjhlcXZhWlBjWEZGSVhYU25WUkR5aStjYnow?= =?utf-8?B?bjk4V0J5UU4yU3hqRlJ0UUNTUDYrRCt5TzBoNlpnSytSY2Jmb2hydVo3VFk3?= =?utf-8?B?VFlxT0tGSGh2bXFhcjBYKytQaFhQOEZYNllDcWFqRndZTHJuRG5vQzJoRG1t?= =?utf-8?B?ZktoWEZ3MkJDVFZKdSt0Q3BQbTlVaVdSZUlFbzNUekZUZGRzNW8vY0NPY1JP?= =?utf-8?B?YU1XRGJVdWh0MUliY1dCV2dLT3JGa2RodEk5eFN2Ulh3aGdrc3ZTLzEwN3RV?= =?utf-8?B?RS9DUVhzcklGNFVJWjllM0EzVFlhVVNzRC9nM0xrMzFpMVhuU0k4cnJxN0RE?= =?utf-8?B?QitOQ2sxNnJMeE4ybDFMNDU0M0gySTAwdHlYOEtyT3EyVnp5d2FjbEtocm1O?= =?utf-8?B?KzNrSlBSeXE4NHZQbFNNKzlSak56K1N0VkZsVCtpQWNJVklEeDhlSGVxRUJj?= =?utf-8?B?c3VIZ1RtMUx2NHRWamk4U1RWMndySEloL1gwTFlsTHRUb1N6dUVBQ2ZPbWly?= =?utf-8?B?S0dpc2dpSUh2dnFHdVpaQ1ZOYmkzT2ZValRCMjlJbnRyUzJEZ3oxeHFGRjAx?= =?utf-8?B?OTJzWWVkUXErQnJYNGRPa09QSkdxcGJtU1JDL1BvSzlNekFEZXVGRzY5MkM5?= =?utf-8?B?MDNuUW1yalRKUFhUVXB3dDU3cE5WbmlZUlJ0N3hEQXgxb0MxWW1VR3JmeTZy?= =?utf-8?B?SHFHNVdTMmpPS2RES1l6ZWlrM1VpNVdYY3FUQ3JlUXc2eHM4OXM4UWdpbExj?= =?utf-8?B?ZE0vdHJjTW0rQWZsUkVkUWFraTZXeEhGTUFJMWpKQkY4UlVuV3R2SlFWSmFz?= =?utf-8?B?YzFuN0lrdkljazdaZkZPamVkUTVBQk1pQnJIUmxpbnVVV2Rhemp2K1V4MmdD?= =?utf-8?B?VEQxRm9IV05nL0poY2lSMkpvQ0lzSnhuZFJyQ3dUUUVTb3ZhMTNxY0RqVDE3?= =?utf-8?B?WlZzb0RFRmg5NzVxaVp4QTR6SElBdlA3QnBPY1N0SG5GM3ZIMEdaakRWKzNz?= =?utf-8?B?eFJOZXREUHErU1VBT2xxNzFBb1BaQUZtZ1Q0ZTF1bTJNc2wxNWpNQUNtWms5?= =?utf-8?B?V3RiYVhUWXZkT1BxR0ZzdG9YbjIwWDhCWGk1L3BLNUlod0FNTUtENFo0SmJW?= =?utf-8?B?ckV3cDQ1Mjl5aGttd3pQNVJ5M25OTWRndXlSam1pQTg3WWYrVWV4WXNwQyt5?= =?utf-8?B?R2VzSS92QS94dlRSeUs1Y3Mvb2JoeU1tWlAvb0dlWGlmY0ttTjhhNEJQcGNT?= =?utf-8?B?aFRBM1duMHVmV3EyRVkzdHFocVk5TWxrckluaktQdGxCclgvVi9VNTAzdFY4?= =?utf-8?B?Nk9xY3JvQ2FXSFN2N3BwbjRmTkZIK2VodkhrNDFRMHd6RWZwaXZFQmRJV01G?= =?utf-8?B?Wk4yT21uSm53MEpoM1MzZitGL21JYXFrOE1iR0RzaElwUnNQazJRNERUMkVD?= =?utf-8?B?TExYNG5ySkF4eENhTXV4dXFNVDBjVm9NbnhqTUFVaEQzaXNxUmVKZ1B2Uzg3?= =?utf-8?B?Y2ZqTVNXdExHOGhDSERXaE0zdTVCWXVoZkdma2oycGwveXBhbjV1aHJ4cU9T?= =?utf-8?B?OG5VK3U4T3BtYlNFQ0pMMHg4bVRhWEd2VzBkNDFpZmx5ZEdHWGd6Sy9VeEpY?= =?utf-8?B?K1NhbWVBMU03QmthY09TZVZkK3pVNGhnY2h5NllkaFFFQ0ZHbk95OHpoTTJB?= =?utf-8?B?RW0vUDdXby80bXVPVjBXRVZldlhoUWNWNzNGSUpCa2N0ZzM4R05DaGREd1p3?= =?utf-8?B?TFBiQk5JdEhiakRzYTZQZjFQY2lxQ080WENFaTJTYnZMNm1OMkdIc0IwYXFq?= =?utf-8?B?VFh4SzVtR0QvYUN5Rng0Q3lvd1M4TS9sRTZsS0VkNFlSTGlLRmtqWldzSmVY?= =?utf-8?B?Rm45ZE5EWUVLY1NkaHdKd2VQcXZ6U1htci96dnlRNGpkOE1ZQWw1U0RrWGxu?= =?utf-8?B?SjF1YTJLRVZqbC9BNnU4ckF3b0czZE9Sd3FoZFNWOFBOUDJIOGlJdk84Tm8r?= =?utf-8?B?L2ErRUNEMmtKY0J0NG4vWU9VSDUraWJkUGVLcmNZZFJKaC9RL244VmhiRW9P?= =?utf-8?B?MmFZS1V5aVArd2M0SHNST21xQk5ENWtPbkdoS3dvM284YU14M0RYaTVsMTNO?= =?utf-8?Q?3TDcMh2r1rCOAsJLPTbyXt5dM?= X-OriginatorOrg: siemens.com X-MS-Exchange-CrossTenant-Network-Message-Id: 1a654b5e-4727-4e22-2845-08dd7c0744c3 X-MS-Exchange-CrossTenant-AuthSource: AS4PR10MB6181.EURPRD10.PROD.OUTLOOK.COM X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 15 Apr 2025 10:21:21.8414 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 38ae3bcd-9579-4fd4-adda-b42e1495d55a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: +mPvi04IpE3FxCIQZffizRv3lkj78DpmEMs3C4+x7WnKN1JOnY/ueDVelRIdsiJmuwCLj9ufIYJErS5YguyTeg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: PR3PR10MB4030 On 15.04.25 10:45, K Prateek Nayak wrote: > (+ Sebastian) > > Hello Jan, > > On 4/15/2025 11:39 AM, Jan Kiszka wrote: >>>> Attached the bits with which we succeeded, sometimes. Setup: Debian 12, >>>> RT kernel, 2-4 cores VM, 1-5 instances of the test, 2 min - 2 h >>>> patience. As we have to succeed with at least 3 race conditions in a >>>> row, that is still not bad... But maybe someone has an idea how to >>>> increase probabilities further. >>> >>> Looking at run.sh, there are only fair tasks with one of them being run >>> with cfs bandwidth constraints. Are you saying something goes wrong on >>> PREEMPT_RT as a result of using bandwidth control on fair tasks? >> >> Yes, exactly. Also our in-field workload that triggers (most likely) >> this issue is not using RT tasks itself. Only kernel threads are RT here. >> >>> >>> What exactly is the symptom you are observing? Does one of the assert() >>> trip during the run? Do you see a stall logged on dmesg? Can you provide >>> more information on what to expect in this 2min - 2hr window? >> >> I've just lost my traces from yesterday ("you have 0 minutes to find a >> power adapter"), but I got nice RCU stall warnings in the VM, including >> backtraces from the involved tasks (minus the read-lock holder IIRC). >> Maybe Florian can drop one of his dumps. > > So I ran your reproducer on a 2vCPU VM running v6.15-rc1 PREEMPT_RT > and I saw: > >     rcu: INFO: rcu_preempt self-detected stall on CPU >     rcu:     0-...!: (15000 ticks this GP) idle=8a74/0/0x1 softirq=0/0 > fqs=0 >     rcu:     (t=15001 jiffies g=12713 q=24 ncpus=2) >     rcu: rcu_preempt kthread timer wakeup didn't happen for 15000 > jiffies! g12713 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 >     rcu:     Possible timer handling issue on cpu=0 timer-softirq=17688 >     rcu: rcu_preempt kthread starved for 15001 jiffies! g12713 f0x0 > RCU_GP_WAIT_FQS(5) ->state=0x402 ->cpu=0 >     rcu:     Unless rcu_preempt kthread gets sufficient CPU time, OOM is > now expected behavior. >     rcu: RCU grace-period kthread stack dump: >     task:rcu_preempt     state:I stack:0     pid:17    tgid:17    > ppid:2      task_flags:0x208040 flags:0x00004000 >     Call Trace: >      >      __schedule+0x401/0x15a0 >      ? srso_alias_return_thunk+0x5/0xfbef5 >      ? lock_timer_base+0x77/0xb0 >      ? srso_alias_return_thunk+0x5/0xfbef5 >      ? __pfx_rcu_gp_kthread+0x10/0x10 >      schedule+0x27/0xd0 >      schedule_timeout+0x76/0x100 >      ? __pfx_process_timeout+0x10/0x10 >      rcu_gp_fqs_loop+0x10a/0x4b0 >      rcu_gp_kthread+0xd3/0x160 >      kthread+0xff/0x210 >      ? rt_spin_lock+0x3c/0xc0 >      ? __pfx_kthread+0x10/0x10 >      ret_from_fork+0x34/0x50 >      ? __pfx_kthread+0x10/0x10 >      ret_from_fork_asm+0x1a/0x30 >      >     CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted 6.15.0-rc1-test- > dirty #746 PREEMPT_{RT,(full)} >     Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS > rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014 >     RIP: 0010:pv_native_safe_halt+0xf/0x20 >     Code: 22 df e9 1f 08 e5 fe 0f 1f 40 00 90 90 90 90 90 90 90 90 90 90 > 90 90 90 90 90 90 f3 0f 1e fa eb 07 0f 00 2d 85 96 15 00 fb f4 f7 > 07 e5 fe 66 66 2e 0f 1f 84 00 00 00 00 00 90 90 90 90 90 90 >     RSP: 0018:ffffffff95803e50 EFLAGS: 00000216 >     RAX: ffff8e2d61534000 RBX: 0000000000000000 RCX: 0000000000000000 >     RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00000000081f8a6c >     RBP: ffffffff9581d280 R08: 0000000000000000 R09: ffff8e2cf7d32301 >     R10: ffff8e2be11ae5c8 R11: 0000000000000001 R12: 0000000000000000 >     R13: 0000000000000000 R14: 0000000000000000 R15: 00000000000147b0 >     FS:  0000000000000000(0000) GS:ffff8e2d61534000(0000) > knlGS:0000000000000000 >     CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >     CR2: 000055e77c3a5128 CR3: 000000010ff78003 CR4: 0000000000770ef0 >     PKRU: 55555554 >     Call Trace: >      >      default_idle+0x9/0x20 >      default_idle_call+0x30/0x100 >      do_idle+0x20f/0x250 >      ? do_idle+0xb/0x250 >      cpu_startup_entry+0x29/0x30 >      rest_init+0xde/0x100 >      start_kernel+0x733/0xb20 >      ? copy_bootdata+0x9/0xb0 >      x86_64_start_reservations+0x18/0x30 >      x86_64_start_kernel+0xba/0x110 >      common_startup_64+0x13e/0x141 >      > > Is this in line with what you are seeing? > Yes, and if you wait a bit longer for the second reporting round, you should get more task backtraces as well. Jan -- Siemens AG, Foundational Technologies Linux Expert Center