Re: linux-next: boot warning from the final tree

[Nathan Chancellor <nathan@kernel.org>]

On Mon, Nov 17, 2025 at 08:22:14PM +1100, Stephen Rothwell wrote:
> Hi all,
> 
> Today's linux-next qemu boot (powerpc pseries_le_defconfig) produced
> this warning:
> 
>   ftrace: allocating 48915 entries in 288 pages
>   ftrace: allocated 287 pages with 6 groups
>   ------------[ cut here ]------------
>   DEBUG_LOCKS_WARN_ON(lock->magic != lock)
>   WARNING: kernel/locking/mutex.c:156 at mutex_lock+0xcc/0x100, CPU#0: swapper/0/0
>   Modules linked in:
>   CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted 6.18.0-rc6-09359-g921087e37218 #1 VOLUNTARY 
>   Hardware name: IBM pSeries (emulated by qemu) POWER9 (architected) 0x4e1202 0xf000005 of:SLOF,HEAD hv:linux,kvm pSeries
>   NIP:  c00000000148041c LR: c000000001480418 CTR: 0000000000000000
>   REGS: c000000002957a10 TRAP: 0700   Not tainted  (6.18.0-rc6-09359-g921087e37218)
>   MSR:  8000000002021033 <SF,VEC,ME,IR,DR,RI,LE>  CR: 24022240  XER: 00000000
>   CFAR: c00000000021123c IRQMASK: 3 
>   GPR00: c000000001480418 c000000002957cb0 c000000001a3a100 0000000000000028 
>   GPR04: 00000000ffffe04a c0000000026abe88 0000000000000001 000000000000004b 
>   GPR08: c0000000026abd28 0000000000000000 0000000000000000 0000000044022240 
>   GPR12: 0000000000000000 c000000002ae9000 0000000000000000 0000000001bff430 
>   GPR16: 000000007e68f070 c00000007f79c480 c000000002969160 c000000002a0f5d8 
>   GPR20: c0000000026a1138 c0000000026a1120 0000000000000000 c0000000019541b8 
>   GPR24: c00000000218a480 c00000000296e1d0 000000007d612000 c00000000380be10 
>   GPR28: c00000000380be20 c00000000380be00 c000000002640100 c00000000380be20 
>   NIP [c00000000148041c] mutex_lock+0xcc/0x100
>   LR [c000000001480418] mutex_lock+0xc8/0x100
>   Call Trace:
>   [c000000002957cb0] [c000000001480418] mutex_lock+0xc8/0x100 (unreliable)
>   [c000000002957d20] [c00000000024a60c] alloc_workqueue_noprof+0x38c/0x8ec
>   [c000000002957e00] [c00000000203018c] workqueue_init_early+0x4d8/0x6ec
>   [c000000002957f30] [c000000002004448] start_kernel+0x74c/0xa4c
>   [c000000002957fe0] [c00000000000e99c] start_here_common+0x1c/0x20
>   Code: 4182ffb4 3d2200f3 392971e4 81290000 2c090000 4082ffa0 3c82ffe0 3c62ffe0 3884bfe0 3863bf68 4ad90d45 60000000 <0fe00000> 4bffff80 60000000 60000000 
>   ---[ end trace 0000000000000000 ]---
>   rcu: Hierarchical RCU implementation.
> 
> I have no idea what caused this.

I noticed this warning in my QEMU boot tests as well and bisected it
down to commit 3572e2edc7b6 ("locking/mutex: Redo __mutex_init()").

  $ make -skj"$(nproc)" ARCH=powerpc CROSS_COMPILE=powerpc64-linux- clean ppc64le_guest_defconfig zImage.epapr

  $ curl -LSs https://github.com/ClangBuiltLinux/boot-utils/releases/download/20241120-044434/ppc64le-rootfs.cpio.zst | zstd -d >rootfs.cpio

  $ qemu-system-ppc64 \
      -display none \
      -nodefaults \
      -device ipmi-bmc-sim,id=bmc0 \
      -device isa-ipmi-bt,bmc=bmc0,irq=10 \
      -machine powernv \
      -kernel arch/powerpc/boot/zImage.epapr \
      -initrd rootfs.cpio \
      -m 2G \
      -serial mon:stdio
  ...
  [    0.000000][    T0] Linux version 6.18.0-rc2-00016-g3572e2edc7b6 (nathan@ax162) (powerpc64-linux-gcc (GCC) 15.2.0, GNU ld (GNU Binutils) 2.45) #1 SMP Fri Nov 21 13:55:26 MST 2025
  ...
  [    0.000000][    T0] ------------[ cut here ]------------
  [    0.000000][    T0] DEBUG_LOCKS_WARN_ON(lock->magic != lock)
  [    0.000000][    T0] WARNING: CPU: 0 PID: 0 at kernel/locking/mutex.c:156 mutex_lock+0xd4/0x100
  [    0.000000][    T0] Modules linked in:
  [    0.000000][    T0] CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted 6.18.0-rc2-00016-g3572e2edc7b6 #1 VOLUNTARY
  [    0.000000][    T0] Hardware name: IBM PowerNV (emulated by qemu) POWER10 0x801200 opal:v7.1-106-g785a5e307 PowerNV
  [    0.000000][    T0] NIP:  c0000000014b2974 LR: c0000000014b2970 CTR: 0000000000000000
  [    0.000000][    T0] REGS: c0000000029979f0 TRAP: 0700   Not tainted  (6.18.0-rc2-00016-g3572e2edc7b6)
  [    0.000000][    T0] MSR:  9000000002021033 <SF,HV,VEC,ME,IR,DR,RI,LE>  CR: 24000220  XER: 00000000
  [    0.000000][    T0] CFAR: c00000000021ed7c IRQMASK: 3
  [    0.000000][    T0] GPR00: c0000000014b2970 c000000002997c90 c000000001a78100 0000000000000028
  [    0.000000][    T0] GPR04: 00000000ffffe04a c0000000026ed958 0000000000000001 000000000000004b
  [    0.000000][    T0] GPR08: c0000000026ed7f0 0000000000000000 0000000000000000 0000000044000220
  [    0.000000][    T0] GPR12: c0000000026ed880 c000000002ba0000 0000000000000018 0000000000000000
  [    0.000000][    T0] GPR16: 0000000000000000 c0000000026e2b88 c0000000026e2ba0 c00000007be5a400
  [    0.000000][    T0] GPR20: c0000000029ed0e0 c000000002aaf7e0 0000000000000000 c0000000019911b8
  [    0.000000][    T0] GPR24: c0000000021ca400 c0000000029f2150 0000000079c90000 c000000003081410
  [    0.000000][    T0] GPR28: c000000003081420 c000000003081400 c0000000021cce98 c000000003081420
  [    0.000000][    T0] NIP [c0000000014b2974] mutex_lock+0xd4/0x100
  [    0.000000][    T0] LR [c0000000014b2970] mutex_lock+0xd0/0x100
  [    0.000000][    T0] Call Trace:
  [    0.000000][    T0] [c000000002997c90] [c0000000014b2970] mutex_lock+0xd0/0x100 (unreliable)
  [    0.000000][    T0] [c000000002997d10] [c000000000258ddc] alloc_workqueue_noprof+0x44c/0x8c8
  [    0.000000][    T0] [c000000002997df0] [c00000000203080c] workqueue_init_early+0x4e4/0x700
  [    0.000000][    T0] [c000000002997f30] [c000000002004388] start_kernel+0x638/0x938
  [    0.000000][    T0] [c000000002997fe0] [c00000000000e99c] start_here_common+0x1c/0x20
  [    0.000000][    T0] Code: 4182ffa8 3d2200f8 3929d134 81290000 2c090000 4082ff94 3c82ffde 3c62ffde 38846d98 38636d20 4ad6c32d 60000000 <0fe00000> e9410068 4bffff70 38210080
  [    0.000000][    T0] ---[ end trace 0000000000000000 ]---
  ...

At the parent change, there is no warning.

Cheers,
Nathan