sparc: crash when using initrd > 5M

[Corentin Labbe <clabbe.montjoie@gmail.com>]

Hello

When using an initrd > 5M, I hit the following kernel crash:
qemu-system-sparc -kernel vmlinux -initrd rootfs.cpio.gz -nographic
Configuration device id QEMU version 1 machine id 32
Probing SBus slot 0 offset 0
Probing SBus slot 1 offset 0
Probing SBus slot 2 offset 0
Probing SBus slot 3 offset 0
Probing SBus slot 4 offset 0
Probing SBus slot 5 offset 0
Invalid FCode start byte
CPUs: 1 x FMI,MB86904
UUID: 00000000-0000-0000-0000-000000000000
Welcome to OpenBIOS v1.1 built on Oct 5 2018 08:20
  Type 'help' for detailed information
[sparc] Kernel already loaded
switching to new context:
PROMLIB: obio_ranges 1
[    0.000000] PROMLIB: Sun Boot Prom Version 3 Revision 2
[    0.000000] Linux version 4.20.0-next-20190102+ (compile@Red) (gcc version 7.3.0 (Gentoo 7.3.0-r3 p1.4)) #148 Thu Jan 3 16:17:08 CET 2019
[    0.000000] printk: bootconsole [earlyprom0] enabled
[    0.000000] ARCH: SUN4M
[    0.000000] TYPE: SPARCstation 5
[    0.000000] Ethernet address: 52:54:00:12:34:56
[    0.000000] Unable to handle kernel NULL pointer dereference
[    0.000000] tsk->{mm,active_mm}->context = ffffffff
[    0.000000] tsk->{mm,active_mm}->pgd = 00000000
[    0.000000]               \|/ ____ \|/
[    0.000000]               "@'/ ,. \`@"
[    0.000000]               /_| \__/ |_\
[    0.000000]                  \__U_/
[    0.000000] swapper(0): Oops [#1]
[    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 4.20.0-next-20190102+ #148
[    0.000000] PSR: 04001fc0 PC: f0010ef0 NPC: f0010ef4 Y: 00000000    Not tainted
[    0.000000] PC: <do_sparc_fault+0x158/0x404>
[    0.000000] %G: 0000000a 000003c4  f05ece08 f05ecc00  00000000 00e00000  f05d4000 00000001
[    0.000000] %O: 00000000 00e00000  00800000 00e00000  00000000 00000002  f05d5bb8 f00bba58
[    0.000000] RPC: <memblock_reserve+0x38/0x68>
[    0.000000] %L: 00000040 f05dfaf8  f05d5c68 00000001  0003ffff 006951e0  f05ed014 f0674ab4
[    0.000000] %I: f05d5c80 00000000  00000002 f1000000  ffffffff 00000000  f05d5c20 f0007fd8
[    0.000000] Disabling lock debugging due to kernel taint
[    0.000000] Caller[f0007fd8]: srmmu_fault+0x58/0x68
[    0.000000] Caller[f0618598]: memblock_alloc_try_nid+0xb8/0xc8
[    0.000000] Caller[f0611094]: srmmu_paging_init+0x174/0xaf8
[    0.000000] Caller[f06106a8]: paging_init+0x4/0x24
[    0.000000] Caller[f060e4f0]: setup_arch+0x3e8/0x480
[    0.000000] Caller[f060ab50]: start_kernel+0x48/0x460
[    0.000000] Caller[f060a43c]: continue_boot+0x324/0x334
[    0.000000] Caller[00000000]:   (null)
[    0.000000] Instruction DUMP:
[    0.000000]  c800a024 
[    0.000000]  83286002 
[    0.000000]  073c17b3 
[    0.000000] <c4010001>
[    0.000000]  c600e22c 
[    0.000000]  8a08a003 
[    0.000000]  80a16001 
[    0.000000]  0280003b 
[    0.000000]  c600c001 
[    0.000000] 
[    0.000000] Kernel panic - not syncing: Attempted to kill the idle task!
[    0.000000] Press Stop-A (L1-A) from sun keyboard or send break
[    0.000000] twice on console to return to the boot prom
[    0.000000] ---[ end Kernel panic - not syncing: Attempted to kill the idle task! ]---
qemu-system-sparc: terminating on signal 15 from pid 13043 (killall)

The NULL ptr dereference is done by memset() in srmmu_nocache_init() and memblock_alloc_try_nid().
If I comment both memset, the boot pass

But since nothing explain the NULL ptr deref in memset(), I suspect something is overriden by the initrd

Regards