Message-ID: <c4724b40-89f6-5aa7-720d-c4a4af57cf45@amazon.com>
Date:   Tue, 13 Jun 2023 11:58:05 -0700
From:   "Bhatnagar, Rishabh" <risbhat@...zon.com>
To:     <bigeasy@...utronix.de>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "sashal@...nel.org" <sashal@...nel.org>, <luizcap@...zon.com>,
        <abuehaze@...zon.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: Observing RCU stalls in kernel 5.4/5.10/5.15/6.1 stable trees


On 6/13/23 11:49 AM, Bhatnagar, Rishabh wrote:
> Hi Sebastian/Greg
>
> We are seeing RCU stall warnings from recent stable tree updates:
> 5.4.243, 5.10.180, 5.15.113, 6.1.31 onwards.
> This is seen in the upstream stable trees without any downstream patches.
>
> The issue is seen few minutes after booting without any workload.
> We launch hundred's of virtual instances and this shows up in 1-2 
> instances, so its hard to reproduce.
> Attaching a few stack traces below.
>
> The issue can be seen on virtual and baremetal instances.
> Another interesting point is we only see this on x86 based instances.
> We also did test this on linux-mainline but were not able to reproduce 
> the issue.
> So maybe there's a fixup or related commit that has gone in?
>
> We tried bisecting the stable trees and found that after reverting the
> below commit we couldn't reproduce this in any of the kernels 
> consistently.
>
> tick/common: Align tick period with the HZ tick. [ Upstream commit
> e9523a0d81899361214d118ad60ef76f0e92f71d ]
>
>
> Not exactly sure how this commit is affecting all stable kernels.
> Can you take a look at this issue and share your insight?
>
> A few example stack traces of the observed RCU stall.
>
> Seen in kernel-5.10.181:
>
> rcu: INFO: rcu_sched self-detected stall on CPU
> rcu: 37-....: (1818 ticks this GP) idle=cf2/1/0x4000000000000000
> softirq=151/151 fqs=7245
>   (t=14809 jiffies g=-759 q=3290)
> NMI backtrace for cpu 37
> Hardware name: Xen HVM domU, BIOS 4.11.amazon 08/24/2006
> Call Trace:
>   <IRQ>
>   dump_stack+0x57/0x70
>   ? lapic_can_unplug_cpu.cold+0x3a/0x3a
>   nmi_cpu_backtrace.cold+0x32/0x68
>   nmi_trigger_cpumask_backtrace+0xdf/0xe6
>   rcu_dump_cpu_stacks+0xa5/0xd7
>   print_cpu_stall.cold+0xa4/0x149
>   check_cpu_stall+0xee/0x210
>   rcu_pending+0x26/0xc0
>   rcu_sched_clock_irq+0x43/0x110
>   update_process_times+0x8c/0xc0
>   tick_periodic+0x27/0x80
>   tick_handle_periodic+0x20/0x70
>   xen_timer_interrupt+0x1e/0x30
>   __handle_irq_event_percpu+0x3d/0x160
>   handle_irq_event_percpu+0x31/0x80
>   handle_percpu_irq+0x37/0x60
>   generic_handle_irq+0x4b/0x60
>   evtchn_2l_handle_events+0x26d/0x280
>   __xen_evtchn_do_upcall+0x66/0xb0
>   __sysvec_xen_hvm_callback+0x22/0x30
>   asm_call_irq_on_stack+0x12/0x20
>   </IRQ>
>   sysvec_xen_hvm_callback+0x72/0x80
>   asm_sysvec_xen_hvm_callback+0x12/0x20
> RIP: 0010:_raw_spin_unlock_irqrestore+0xe/0x20
> RSP: 0000:ffffc900188ffa28 EFLAGS: 00000246
>   pci_conf1_read+0xa4/0x100
>   pci_bus_read_config_byte+0x3f/0x70
>   __pci_find_next_cap_ttl+0x3b/0xd0
>   pci_find_capability+0x71/0xa0
>   pci_pm_init+0x6c/0x1c0
>   ? pci_allocate_vc_save_buffers+0x6d/0x8b
>   pci_device_add+0xb0/0x1b0
>   pci_scan_single_device+0xbd/0xf0
>   pci_scan_slot+0x53/0x120
>   pci_scan_child_bus_extend+0x3a/0x2a0
>   acpi_pci_root_create+0x20c/0x26a
>   pci_acpi_scan_root+0x19a/0x1c0
>   ? negotiate_os_control+0xdd/0x2b9
>   acpi_pci_root_add.cold+0x59/0x1b0
>   acpi_bus_attach+0xee/0x210
>   acpi_bus_attach+0x63/0x210
>   acpi_bus_attach+0x63/0x210
>   acpi_bus_scan+0x43/0x90
>   ? acpi_bus_init+0x15f/0x15f
>   acpi_scan_init+0x10e/0x1b4
>   acpi_init+0xba/0x11d
>   ? intel_idle_init+0x2a2/0x2a2
>   do_one_initcall+0x44/0x1c4
>   do_initcalls+0xc6/0xdf
>   kernel_init_freeable+0x14d/0x198
>   ? rest_init+0xb4/0xb4
>   kernel_init+0xa/0x11c
>   ret_from_fork+0x22/0x30
>
> Seen in kernel-5.4.246:
>
> NMI backtrace for cpu 7
> CPU: 7 PID: 1 Comm: swapper/0 Not tainted 5.4.246 #1
> Hardware name: Amazon EC2 m5.2xlarge/, BIOS 1.0 10/16/2017
> RIP: 0010:lapic_next_deadline+0x26/0x40
> RSP: 0000:ffffc900001ecf98 EFLAGS: 00000002
> Call Trace:
>  <NMI>
>  ? nmi_cpu_backtrace+0x4c/0x90
>  ? nmi_cpu_backtrace_handler+0xd/0x20
>  ? nmi_handle+0x71/0x160
>  ? default_do_nmi+0x4e/0x100
>  ? do_nmi+0x15b/0x190
>  ? end_repeat_nmi+0x16/0x62
>  ? lapic_next_deadline+0x26/0x40
>  ? lapic_next_deadline+0x26/0x40
>  ? lapic_next_deadline+0x26/0x40
>  </NMI>
>  <IRQ>
>  clockevents_program_event+0xcf/0x100
>  tick_handle_periodic+0x48/0x60
>  smp_apic_timer_interrupt+0x6a/0x130
>  apic_timer_interrupt+0xf/0x20
>  </IRQ>
>  ? vprintk_emit+0x19b/0x280
>  ? printk+0x52/0x6e
>  ? pci_hp_add+0x189/0x300
>  ? acpiphp_register_hotplug_slot+0xe0/0xf0
>  ? acpiphp_add_context+0x3b1/0x460
>  ? acpi_ns_walk_namespace+0x108/0x220
>  ? acpiphp_put_context.part.12+0x30/0x30
>  ? acpi_walk_namespace+0xc8/0xf0
>  ? kmem_cache_alloc_trace+0x1f8/0x210
>  ? acpiphp_enumerate_slots+0x172/0x250
>  ? acpi_pci_add_bus+0x50/0xd0
>  ? pci_register_host_bridge+0x22b/0x460
>  ? pci_create_root_bus+0x87/0xb0
>  ? acpi_pci_root_create+0x128/0x290
>  ? pci_acpi_scan_root+0x14a/0x1b0
>  ? acpi_pci_root_add+0x1ff/0x580
>  ? acpi_evaluate_integer+0x52/0x90
>  ? set_debug_rodata+0x2f/0x2f
>  ? acpi_bus_attach+0x144/0x1d0
>  ? acpi_bus_attach+0x80/0x1d0
>  ? acpi_bus_attach+0x80/0x1d0
>  ? acpi_sleep_proc_init+0x24/0x24
>  ? acpi_sleep_proc_init+0x24/0x24
>  ? acpi_bus_scan+0x43/0x90
>  ? acpi_scan_init+0xf1/0x235
>  ? acpi_sleep_proc_init+0x24/0x24
>  ? acpi_init+0x2e9/0x349
>  ? do_one_initcall+0x46/0x200
>  ? kernel_init_freeable+0x1db/0x286
>  ? rest_init+0xb0/0xb0
>  ? kernel_init+0xa/0x110
>  ? ret_from_fork+0x35/0x40
>
>
> Seen in 5.10.183:
>
> rcu: INFO: rcu_sched detected stalls on CPUs/tasks:
> acpiphp: Slot [19] registered
> rcu:     3-....: (349 ticks this GP) idle=936/1/0x4000000000000000 
> softirq=94/94 fqs=151
>  (detected by 0, t=14752 jiffies, g=-1063, q=591)
> Sending NMI from CPU 0 to CPUs 3:
> NMI backtrace for cpu 3
> CPU: 3 PID: 1 Comm: swapper/0 Not tainted 5.10.183 #1
> Hardware name: Amazon EC2 m5.2xlarge/, BIOS 1.0 10/16/2017
> RIP: 0010:io_serial_in+0x14/0x20
> RSP: 0000:ffffbc9640017720 EFLAGS: 00000006
> PKRU: 55555554
> Call Trace:
>  <NMI>
>  ? nmi_cpu_backtrace+0x57/0xb0
>  ? nmi_cpu_backtrace_handler+0xd/0x20
>  ? nmi_handle+0x62/0x130
>  ? default_do_nmi+0x49/0x100
>  ? exc_nmi+0x152/0x170
>  ? end_repeat_nmi+0x16/0x67
>  ? mem16_serial_in+0x10/0x20
>  ? io_serial_in+0x14/0x20
>  ? io_serial_in+0x14/0x20
>  ? io_serial_in+0x14/0x20
>  </NMI>
>  serial8250_console_write+0x8e/0x310
>  ? record_print_text+0xbf/0x150
>  console_unlock+0x485/0x4c0
>  vprintk_emit+0xe4/0x240
>  printk+0x52/0x72
>  ? pci_hp_add+0x18d/0x300
>  acpiphp_register_hotplug_slot+0xe4/0x100
>  acpiphp_add_context+0x3b5/0x460
>  acpi_ns_walk_namespace+0x10c/0x220
>  ? acpiphp_put_context.part.13+0x30/0x30
>  ? acpiphp_put_context.part.13+0x30/0x30
>  acpi_walk_namespace+0xd4/0xf0
>  ? kmem_cache_alloc_trace+0x3be/0x400
>  acpiphp_enumerate_slots+0x175/0x260
>  acpi_pci_add_bus+0x50/0xe0
>  pci_register_host_bridge+0x233/0x4d0
>  ? complete_all+0x2a/0x40
>  pci_create_root_bus+0x87/0xc0
>  acpi_pci_root_create+0x128/0x2a0
>  pci_acpi_scan_root+0x14e/0x1b0
>  acpi_pci_root_add+0x203/0x580
>  ? acpi_evaluate_integer+0x52/0x90
>  ? rdinit_setup+0x2f/0x2f
>  acpi_bus_attach+0x148/0x1d0
>  acpi_bus_attach+0x84/0x1d0
>  acpi_bus_attach+0x84/0x1d0
>  ? acpi_sleep_proc_init+0x24/0x24
>  ? acpi_sleep_proc_init+0x24/0x24
>  acpi_bus_scan+0x43/0x90
>  acpi_scan_init+0xff/0x247
>  ? acpi_sleep_proc_init+0x24/0x24
>  acpi_init+0x2e9/0x34d
>  do_one_initcall+0x44/0x1e0
>  kernel_init_freeable+0x229/0x286
>  ? rest_init+0xc0/0xc0
>  kernel_init+0xa/0x120
>  ret_from_fork+0x22/0x30
>
> Thanks
> Rishabh
CCing stable kernel list.

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