Subject: linux-next: runtime warning in Linus' tree

From: Stephen Rothwell <[email-masked]>
Date: Thu, 13 Aug 2020 16:46:54 +1000

Hi all,

Testing Linus' tree today, my qemu runs (PowerPC
powerpc_pseries_le_defconfig) produce the following WARNING:

[    0.021401][    T0] Mount-cache hash table entries: 8192 (order: 0, 65536 bytes, linear)
[    0.021529][    T0] Mountpoint-cache hash table entries: 8192 (order: 0, 65536 bytes, linear)
[    0.053969][    T0] ------------[ cut here ]------------
[    0.055220][    T0] WARNING: CPU: 0 PID: 0 at mm/memcontrol.c:5220 mem_cgroup_css_alloc+0x350/0x904
[    0.055355][    T0] Modules linked in:
[    0.055812][    T0] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.8.0 #5
[    0.055976][    T0] NIP:  c000000000410010 LR: c00000000040fd68 CTR: 0000000000000000
[    0.056097][    T0] REGS: c0000000011e7ab0 TRAP: 0700   Not tainted  (5.8.0)
[    0.056162][    T0] MSR:  8000000002029033 <SF,VEC,EE,ME,IR,DR,RI,LE>  CR: 24000888  XER: 00000000
[    0.056449][    T0] CFAR: c00000000040fd80 IRQMASK: 0 
[    0.056449][    T0] GPR00: c00000000040fd68 c0000000011e7d40 c0000000011e8300 0000000000000001 
[    0.056449][    T0] GPR04: 0000000000000228 0000000000000000 0000000000000001 ffffffffffffffff 
[    0.056449][    T0] GPR08: c00000007d003208 0000000000000000 0000000000000000 c00000007d002fe8 
[    0.056449][    T0] GPR12: 0000000000000001 c0000000013d0000 0000000000000000 00000000011dd528 
[    0.056449][    T0] GPR16: 00000000011dd840 00000000011dd690 0000000000000018 0000000000000003 
[    0.056449][    T0] GPR20: 0000000000000001 c0000000010cbcf8 0000000000000003 c0000000010cd540 
[    0.056449][    T0] GPR24: c0000000010e8778 c0000000010e9080 c0000000010cbcd8 0000000000000000 
[    0.056449][    T0] GPR28: 0000000000000000 c00000007e2a1000 c0000000010cbcc8 c00000000118ea00 
[    0.057109][    T0] NIP [c000000000410010] mem_cgroup_css_alloc+0x350/0x904
[    0.057177][    T0] LR [c00000000040fd68] mem_cgroup_css_alloc+0xa8/0x904
[    0.057394][    T0] Call Trace:
[    0.057534][    T0] [c0000000011e7d40] [c00000000040fd68] mem_cgroup_css_alloc+0xa8/0x904 (unreliable)
[    0.057814][    T0] [c0000000011e7dc0] [c000000000f5b13c] cgroup_init_subsys+0xbc/0x210
[    0.057903][    T0] [c0000000011e7e10] [c000000000f5b690] cgroup_init+0x220/0x598
[    0.057973][    T0] [c0000000011e7ee0] [c000000000f34354] start_kernel+0x67c/0x6ec
[    0.058047][    T0] [c0000000011e7f90] [c00000000000cb88] start_here_common+0x1c/0x614
[    0.058241][    T0] Instruction dump:
[    0.058420][    T0] eac10030 eae10038 eb410050 eb610058 4bffff60 60000000 60000000 60000000 
[    0.058550][    T0] 3be00100 4bfffdfc 60000000 60000000 <0fe00000> 4bfffd70 60000000 60000000 
[    0.059381][    T0] ---[ end trace cb2d79b4994ef1fe ]---
[    0.059810][    T0] ------------[ cut here ]------------
[    0.059872][    T0] WARNING: CPU: 0 PID: 0 at mm/memcontrol.c:5135 mem_cgroup_css_alloc+0x750/0x904
[    0.059930][    T0] Modules linked in:
[    0.060053][    T0] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G        W         5.8.0 #5
[    0.060113][    T0] NIP:  c000000000410410 LR: c00000000040ff2c CTR: 0000000000000000
[    0.060171][    T0] REGS: c0000000011e7ab0 TRAP: 0700   Tainted: G        W          (5.8.0)
[    0.060229][    T0] MSR:  8000000002029033 <SF,VEC,EE,ME,IR,DR,RI,LE>  CR: 24000880  XER: 00000000
[    0.060332][    T0] CFAR: c00000000040fe48 IRQMASK: 0 
[    0.060332][    T0] GPR00: c00000000040ff2c c0000000011e7d40 c0000000011e8300 c00000007e234c00 
[    0.060332][    T0] GPR04: 0000000000000000 0000000000000000 c00000007e235000 0000000000000013 
[    0.060332][    T0] GPR08: 000000007ec00000 0000000000000000 0000000000000000 0000000000000001 
[    0.060332][    T0] GPR12: 0000000000000000 c0000000013d0000 0000000000000000 00000000011dd528 
[    0.060332][    T0] GPR16: 00000000011dd840 00000000011dd690 0000000000000018 0000000000000003 
[    0.060332][    T0] GPR20: c000000001223300 c000000000e95900 c00000000118ea00 c0000000012232c0 
[    0.060332][    T0] GPR24: c0000000010e8778 c0000000010e9080 0000000000400cc0 0000000000000000 
[    0.060332][    T0] GPR28: 0000000000000000 c00000007e2a1000 c00000007e234c00 0000000000000000 
[    0.060855][    T0] NIP [c000000000410410] mem_cgroup_css_alloc+0x750/0x904
[    0.060911][    T0] LR [c00000000040ff2c] mem_cgroup_css_alloc+0x26c/0x904
[    0.060958][    T0] Call Trace:
[    0.061003][    T0] [c0000000011e7d40] [c00000000040ff2c] mem_cgroup_css_alloc+0x26c/0x904 (unreliable)
[    0.061081][    T0] [c0000000011e7dc0] [c000000000f5b13c] cgroup_init_subsys+0xbc/0x210
[    0.061165][    T0] [c0000000011e7e10] [c000000000f5b690] cgroup_init+0x220/0x598
[    0.061233][    T0] [c0000000011e7ee0] [c000000000f34354] start_kernel+0x67c/0x6ec
[    0.061303][    T0] [c0000000011e7f90] [c00000000000cb88] start_here_common+0x1c/0x614
[    0.061364][    T0] Instruction dump:
[    0.061408][    T0] ebe1fff8 7c0803a6 4e800020 60000000 60000000 3d220004 e929d230 7c3c4800 
[    0.061508][    T0] 41820190 e93c03d2 4bfffc80 60000000 <0fe00000> 4bfffa38 60000000 60000000 
[    0.061630][    T0] ---[ end trace cb2d79b4994ef1ff ]---
[    0.096387][    T1] EEH: pSeries platform initialized
[    0.097232][    T1] POWER8 performance monitor hardware support registered

[The line numbers in the final linux next are 5226 and 5141 due to
later patches.]

Introduced (or exposed) by commit

  3e38e0aaca9e ("mm: memcg: charge memcg percpu memory to the parent cgroup")

This commit actually adds the WARN_ON, so it either adds the bug that
sets it off, or the bug already existed.

Unfotunately, the version of this patch in linux-next up tuntil today
is different.  :-(

I have left this as I have no idea how to fix it :-)

-- 
Cheers,
Stephen Rothwell