[Qemu-ppc] pseries on qemu-system-ppc64le crashes in doorbell_core_ipi()

[Cédric Le Goater]

On 3/27/19 1:36 PM, Sebastian Andrzej Siewior wrote:
> With qemu-system-ppc64le -machine pseries -smp 4 I get:
> 
> |#  chrt 1 hackbench
> |Running in process mode with 10 groups using 40 file descriptors each (== 400 tasks)
> |Each sender will pass 100 messages of 100 bytes
> | Oops: Exception in kernel mode, sig: 4 [#1]
> | LE PAGE_SIZE=64K MMU=Hash PREEMPT SMP NR_CPUS=2048 NUMA pSeries
> | Modules linked in:
> | CPU: 0 PID: 629 Comm: hackbench Not tainted 5.1.0-rc2 #71
> | NIP:  c000000000046978 LR: c000000000046a38 CTR: c0000000000b0150
> | REGS: c0000001fffeb8e0 TRAP: 0700   Not tainted  (5.1.0-rc2)
> | MSR:  8000000000089033 <SF,EE,ME,IR,DR,RI,LE>  CR: 42000874  XER: 00000000
> | CFAR: c000000000046a34 IRQMASK: 1
> | GPR00: c0000000000b0170 c0000001fffebb70 c000000000a6ba00 0000000028000000
> …
> | NIP [c000000000046978] doorbell_core_ipi+0x28/0x30
> | LR [c000000000046a38] doorbell_try_core_ipi+0xb8/0xf0
> | Call Trace:
> | [c0000001fffebb70] [c0000001fffebba0] 0xc0000001fffebba0 (unreliable)
> | [c0000001fffebba0] [c0000000000b0170] smp_pseries_cause_ipi+0x20/0x70
> | [c0000001fffebbd0] [c00000000004b02c] arch_send_call_function_single_ipi+0x8c/0xa0
> | [c0000001fffebbf0] [c0000000001de600] irq_work_queue_on+0xe0/0x130
> | [c0000001fffebc30] [c0000000001340c8] rto_push_irq_work_func+0xc8/0x120
> …
> | Instruction dump:
> | 60000000 60000000 3c4c00a2 384250b0 3d220009 392949c8 81290000 3929ffff
> | 7d231838 7c0004ac 5463017e 64632800 <7c00191c> 4e800020 3c4c00a2 38425080
> | ---[ end trace eb842b544538cbdf ]---
> 
> and I was wondering whether this is a qemu bug or the kernel is using an
> opcode it should rather not. If I skip doorbell_try_core_ipi() in
> smp_pseries_cause_ipi() then there is no crash. The comment says "POWER9
> should not use this handler" so…

I would say Linux is using a msgsndp instruction which is not implemented
in QEMU TCG. But why have we started using dbells in Linux ? 

C.