linux-stable.git/arch/mips/kernel/smp.c, branch linux-6.18.y

MIPS: smp: report dying CPU to RCU in stop_this_cpu()

2026-07-04T11:44:20+00:00

commit 9f3f3bdc6d9dac1a5a8262ee7ad0f2ff1527a7e7 upstream.

smp_send_stop() parks all secondary CPUs in stop_this_cpu(). The function
marks the CPU offline for the scheduler via set_cpu_online(false) but
never informs RCU, so RCU keeps expecting a quiescent state from CPUs
that are now spinning forever with interrupts disabled.

As long as nothing waits for an RCU grace period after smp_send_stop()
this is harmless, which is why it went unnoticed. Since commit
91840be8f710 ("irq_work: Fix use-after-free in irq_work_single() on PREEMPT_RT")
however, irq_work_sync() calls synchronize_rcu() on architectures without
an irq_work self-IPI, i.e. where arch_irq_work_has_interrupt() returns
false. That is the asm-generic default used by MIPS. Any irq_work_sync()
issued in the reboot/shutdown path after smp_send_stop() then blocks on
a grace period that can never complete, hanging the reboot:

  WARNING: CPU: 0 PID: 15 at kernel/irq_work.c:144 irq_work_queue_on
  ...
  rcu: INFO: rcu_sched detected stalls on CPUs/tasks:
  rcu: Offline CPU 1 blocking current GP.
  rcu: Offline CPU 2 blocking current GP.
  rcu: Offline CPU 3 blocking current GP.

This issue was noticed on several Realtek MIPS switch SoCs (MIPS
interAptiv) and came up during kernel bump downstream in OpenWrt from
6.18.33 to 6.18.34, after the backport of the patch to the 6.18 stable
branch. The patch also has been backported all the way back to 6.1.

Call rcutree_report_cpu_dead() once interrupts are disabled, mirroring the
generic CPU-hotplug offline path, so RCU stops waiting on the parked CPUs
and grace periods can still complete. MIPS shuts down all CPUs here
without going through the CPU-hotplug mechanism, so this report is not
otherwise issued. Reporting a dying CPU to RCU outside the regular hotplug
offline path is not unprecedented: arm64 does the same in cpu_die_early().
There it is an exception for a CPU that was coming online and is aborting
bringup, rather than the default shutdown action as on MIPS.

Fixes: 91840be8f710 ("irq_work: Fix use-after-free in irq_work_single() on PREEMPT_RT")
CC: stable@vger.kernel.org
Signed-off-by: Jonas Jelonek 
Signed-off-by: Thomas Bogendoerfer 
Signed-off-by: Greg Kroah-Hartman

MIPS: SMP: Move the AP sync point before the calibration delay

2025-05-25T13:00:23+00:00

In the calibration delay process, some resources are shared, so it's
better to move it after the parallel execution part. Thanks to the
patch optimizing CPU delay calibration, this change has no impact on
the boot time improvements gained from CPU parallel boot.

Signed-off-by: Gregory CLEMENT 
Signed-off-by: Thomas Bogendoerfer

MIPS: SMP: Move the AP sync point before the non-parallel aware functions

2025-05-20T06:43:24+00:00

When CONFIG_HOTPLUG_PARALLEL is enabled, the code executing before
cpuhp_ap_sync_alive() is executed in parallel, while after it is
serialized. The functions set_cpu_sibling_map() and set_cpu_core_map()
were not designed to be executed in parallel, so by moving the
cpuhp_ap_sync_alive() before cpuhp_ap_sync_alive(), we then ensure
they will be called serialized.

The measurement done on EyeQ5 did not show any relevant boot time
increase after applying this patch.

Fixes: 76c43eb507bc ("MIPS: SMP: Implement parallel CPU bring up for EyeQ")
Reported-by: Huacai Chen 
Signed-off-by: Gregory CLEMENT 
Signed-off-by: Thomas Bogendoerfer

MIPS: SMP: Implement parallel CPU bring up for EyeQ

2025-04-27T07:45:15+00:00

Added support for starting CPUs in parallel on EyeQ to speed up boot time.

On EyeQ5, booting 8 CPUs is now ~90ms faster.
On EyeQ6, booting 32 CPUs is now ~650ms faster.

Signed-off-by: Gregory CLEMENT 
Signed-off-by: Thomas Bogendoerfer

smp: Mark smp_prepare_boot_cpu() __init

2024-09-08T14:01:10+00:00

smp_prepare_boot_cpu() is only called during boot, hence mark it as
__init.

Signed-off-by: Bibo Mao 
Signed-off-by: Thomas Gleixner 
Reviewed-by: Huacai Chen 
Link: https://lore.kernel.org/all/20240907082720.452148-1-maobibo@loongson.cn

MIPS: sync-r4k: Rework based on x86 tsc_sync

2024-07-03T14:50:12+00:00

The original sync-r4k did a good job on reducing jitter by determine
the "next time value", but it has a limitation that when synchronization
being performed too many times due to high core count or CPU hotplug,
the timewrap on CPU0 will become unaccpetable.

Rework the mechanism based on latest x86 tsc_sync. (It seems like
the original implementation is based on tsc_sync at that time,
so it's just a refresh.) To improve overall performance.

Tesed on Loongson64, Boston, QEMU.

Signed-off-by: Jiaxun Yang 
Signed-off-by: Thomas Bogendoerfer

Merge tag 'mm-nonmm-stable-2024-01-09-10-33' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

2024-01-09T19:46:20+00:00

Pull non-MM updates from Andrew Morton:
 "Quite a lot of kexec work this time around. Many singleton patches in
  many places. The notable patch series are:

   - nilfs2 folio conversion from Matthew Wilcox in 'nilfs2: Folio
     conversions for file paths'.

   - Additional nilfs2 folio conversion from Ryusuke Konishi in 'nilfs2:
     Folio conversions for directory paths'.

   - IA64 remnant removal in Heiko Carstens's 'Remove unused code after
     IA-64 removal'.

   - Arnd Bergmann has enabled the -Wmissing-prototypes warning
     everywhere in 'Treewide: enable -Wmissing-prototypes'. This had
     some followup fixes:

      - Nathan Chancellor has cleaned up the hexagon build in the series
        'hexagon: Fix up instances of -Wmissing-prototypes'.

      - Nathan also addressed some s390 warnings in 's390: A couple of
        fixes for -Wmissing-prototypes'.

      - Arnd Bergmann addresses the same warnings for MIPS in his series
        'mips: address -Wmissing-prototypes warnings'.

   - Baoquan He has made kexec_file operate in a top-down-fitting manner
     similar to kexec_load in the series 'kexec_file: Load kernel at top
     of system RAM if required'

   - Baoquan He has also added the self-explanatory 'kexec_file: print
     out debugging message if required'.

   - Some checkstack maintenance work from Tiezhu Yang in the series
     'Modify some code about checkstack'.

   - Douglas Anderson has disentangled the watchdog code's logging when
     multiple reports are occurring simultaneously. The series is
     'watchdog: Better handling of concurrent lockups'.

   - Yuntao Wang has contributed some maintenance work on the crash code
     in 'crash: Some cleanups and fixes'"

* tag 'mm-nonmm-stable-2024-01-09-10-33' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (157 commits)
  crash_core: fix and simplify the logic of crash_exclude_mem_range()
  x86/crash: use SZ_1M macro instead of hardcoded value
  x86/crash: remove the unused image parameter from prepare_elf_headers()
  kdump: remove redundant DEFAULT_CRASH_KERNEL_LOW_SIZE
  scripts/decode_stacktrace.sh: strip unexpected CR from lines
  watchdog: if panicking and we dumped everything, don't re-enable dumping
  watchdog/hardlockup: use printk_cpu_sync_get_irqsave() to serialize reporting
  watchdog/softlockup: use printk_cpu_sync_get_irqsave() to serialize reporting
  watchdog/hardlockup: adopt softlockup logic avoiding double-dumps
  kexec_core: fix the assignment to kimage->control_page
  x86/kexec: fix incorrect end address passed to kernel_ident_mapping_init()
  lib/trace_readwrite.c:: replace asm-generic/io with linux/io
  nilfs2: cpfile: fix some kernel-doc warnings
  stacktrace: fix kernel-doc typo
  scripts/checkstack.pl: fix no space expression between sp and offset
  x86/kexec: fix incorrect argument passed to kexec_dprintk()
  x86/kexec: use pr_err() instead of kexec_dprintk() when an error occurs
  nilfs2: add missing set_freezable() for freezable kthread
  kernel: relay: remove relay_file_splice_read dead code, doesn't work
  docs: submit-checklist: remove all of "make namespacecheck"
  ...

mips: smp: fix setup_profiling_timer() prototype

2023-12-11T01:21:42+00:00

The function is unconditionally defined in smp.c but is conditionally
declared in a header that is not included here.

arch/mips/kernel/smp.c:473:5: error: no previous prototype for 'setup_profiling_timer' [-Werror=missing-prototypes]

Add the missing #include and #ifdef to match the declaration.

Link: https://lkml.kernel.org/r/20231204115710.2247097-20-arnd@kernel.org
Signed-off-by: Arnd Bergmann 
Cc: Stephen Rothwell 
Cc: Thomas Bogendoerfer 
Signed-off-by: Andrew Morton

mips/smp: Call rcutree_report_cpu_starting() earlier

2023-12-05T17:43:05+00:00

rcutree_report_cpu_starting() must be called before
clockevents_register_device() to avoid the following lockdep splat triggered by
calling list_add() when CONFIG_PROVE_RCU_LIST=y:

  WARNING: suspicious RCU usage
  ...
  -----------------------------
  kernel/locking/lockdep.c:3680 RCU-list traversed in non-reader section!!

  other info that might help us debug this:

  RCU used illegally from offline CPU!
  rcu_scheduler_active = 1, debug_locks = 1
  no locks held by swapper/1/0.
  ...
  Call Trace:
  [] show_stack+0x64/0x158
  [] dump_stack_lvl+0x90/0xc4
  [] __lock_acquire+0x1404/0x2940
  [] lock_acquire+0x14c/0x448
  [] _raw_spin_lock_irqsave+0x50/0x88
  [] clockevents_register_device+0x60/0x1e8
  [] r4k_clockevent_init+0x220/0x3a0
  [] start_secondary+0x50/0x3b8

raw_smp_processor_id() is required in order to avoid calling into lockdep
before RCU has declared the CPU to be watched for readers.

See also commit 29368e093921 ("x86/smpboot:  Move rcu_cpu_starting() earlier"),
commit de5d9dae150c ("s390/smp: move rcu_cpu_starting() earlier") and commit
99f070b62322 ("powerpc/smp: Call rcu_cpu_starting() earlier").

Signed-off-by: Stefan Wiehler 
Reviewed-by: Huacai Chen 
Signed-off-by: Thomas Bogendoerfer

Merge tag 'mips_6.5' of git://git.kernel.org/pub/scm/linux/kernel/git/mips/linux

2023-06-29T22:01:51+00:00

Pull MIPS updates from Thomas Bogendoerfer:

 - add support for TP-Link HC220 G5 v1

 - add support for Wifi/Bluetooth on CI20

 - rework Ralink clock and reset handling

 - cleanups and fixes

* tag 'mips_6.5' of git://git.kernel.org/pub/scm/linux/kernel/git/mips/linux: (58 commits)
  MIPS: Loongson64: DTS: Add RTC support to Loongson-2K1000
  MIPS: Loongson64: DTS: Add RTC support to LS7A PCH
  MIPS: OCTEON: octeon-usb: cleanup divider calculation
  MIPS: OCTEON: octeon-usb: introduce dwc3_octeon_{read,write}q
  MIPS: OCTEON: octeon-usb: move gpio config to separate function
  MIPS: OCTEON: octeon-usb: use bitfields for shim register
  MIPS: OCTEON: octeon-usb: use bitfields for host config register
  MIPS: OCTEON: octeon-usb: use bitfields for control register
  MIPS: OCTEON: octeon-usb: add all register offsets
  mips: ralink: match all supported system controller compatible strings
  MIPS: dec: prom: Address -Warray-bounds warning
  MIPS: DTS: CI20: Raise VDDCORE voltage to 1.125 volts
  clk: ralink: mtmips: Fix uninitialized use of ret in mtmips_register_{fixed,factor}_clocks()
  mips: ralink: introduce commonly used remap node function
  mips: pci-mt7620: use dev_info() to log PCIe device detection result
  mips: pci-mt7620: do not print NFTS register value as error log
  MAINTAINERS: add Mediatek MTMIPS Clock maintainer
  mips: ralink: get cpu rate from new driver code
  mips: ralink: remove reset related code
  mips: ralink: mt7620: remove clock related code
  ...