WARN_ONCE does not warn once

Hello,

on powernv with 5.3.8 kernel I get flood of messages on boot.

The messages match WARN_ONCE(1, "opal: OPAL_CONSOLE_FLUSH missing.\n");

------------[ cut here ]------------
opal: OPAL_CONSOLE_FLUSH missing.
WARNING: CPU: 0 PID: 0 at ../arch/powerpc/platforms/powernv/opal.c:435 __opal_flush_console+0xfc/0x110
Modules linked in:
Supported: No, Unreleased kernel
CPU: 0 PID: 0 Comm: swapper Not tainted 5.3.8-11.gea9b07d-default #1 SLE15-SP2 (unreleased)
NIP:  c0000000000b9b9c LR: c0000000000b9b98 CTR: c000000000c06ca0
REGS: c00000000158b8c0 TRAP: 0700   Not tainted  (5.3.8-11.gea9b07d-default)
MSR:  9000000000021033 <SF,HV,ME,IR,DR,RI,LE>  CR: 28004222  XER: 20000000
CFAR: c000000000132df0 IRQMASK: 1 
GPR00: c0000000000b9b98 c00000000158bb50 c00000000158c600 0000000000000022 
GPR04: c000000000e63b7a 0000000000000002 4f534e4f435f4c41 4853554c465f454c 
GPR08: 676e697373696d20 0000000000000000 0000000000000027 9000000000001033 
GPR12: c0000000001cc080 c000000002150000 0000000000000000 0000000000000000 
GPR16: 00003ffff13114c0 0000000000000000 c0000000014641e0 0000000000000000 
GPR20: 0000000000000000 c000000001765738 c000000001763738 0000000000000001 
GPR24: c0000000015c1ed8 c000000001763318 c000000001762dec 0000000000000001 
GPR28: 0000000000000000 c000000002130d18 0000000000000000 0000000000000000 
NIP [c0000000000b9b9c] __opal_flush_console+0xfc/0x110
LR [c0000000000b9b98] __opal_flush_console+0xf8/0x110
Call Trace:
[c00000000158bb50] [c0000000000b9b98] __opal_flush_console+0xf8/0x110 (unreliable)
[c00000000158bbd0] [c0000000000b9dbc] opal_flush_console+0x2c/0x60
[c00000000158bc00] [c00000000080c180] udbg_opal_putc+0x80/0xd0
[c00000000158bc50] [c000000000033660] udbg_write+0x90/0x140
[c00000000158bc90] [c0000000001c888c] console_unlock+0x32c/0x820
[c00000000158bd70] [c0000000001c9768] register_console+0x5d8/0x790
[c00000000158be10] [c000000000fb9dcc] register_early_udbg_console+0x9c/0xb4
[c00000000158be80] [c000000000fb99c8] setup_arch+0x78/0x39c
[c00000000158bef0] [c000000000fb3c00] start_kernel+0xb4/0x6bc
[c00000000158bf90] [c00000000000c4d4] start_here_common+0x1c/0x20
Instruction dump:
60000000 3860fffe 4bffffa8 60000000 60000000 3c62ff8d 39200001 3d42fff6 
38637558 992afea8 480791f5 60000000 <0fe00000> 4bffff54 48079715 60000000 
random: get_random_bytes called from print_oops_end_marker+0x6c/0xa0 with crng_init=0
---[ end trace 0000000000000000 ]---

This is reapated numerous times and the kernel eventually boots.

Is that an issue with the WARN_ONCE implementation?

Thanks

Michal