[PATCH] arm64: add dump_stack to show_regs

[Ding Tianhong]

Recently I found that when the system trigger a soft lockup in interrupt,
there is only showing the regs, but no stack trace, it is very difficult
to locate the problem:

===========================================

[10072.999437] NMI watchdog: BUG: soft lockup - CPU#16 stuck for 23s! [ksoftirqd/16:88]
.....
[10073.041254] CPU: 16 PID: 88 Comm: ksoftirqd/16 Tainted: G 4.x.x #1
[10073.041258] Hardware name: xxxxx, BIOS 1.17 01/04/2017
[10073.041261] task: ffff803f6cb06200 ti: ffff803f6cb50000 task.ti: ffff803f6cb50000
[10073.041274] PC is at _raw_spin_unlock_irqrestore+0x24/0x30
[10073.041280] LR is at blk_run_queue+0x3c/0x48
[10073.041282] pc : [<ffff800000a3df14>] lr : [<ffff8000004f3a7c>] pstate: 60000145
[10073.041285] sp : ffff803f6cb53b20
[10073.041286] x29: ffff803f6cb53b20 x28: 0000000000001000
[10073.041290] x27: 0000000000000000 x26: ffff800001226000
[10073.041294] x25: 0000000000000000 x24: 0000000000000140
[10073.041297] x23: ffff803f62e108c8 x22: ffff800001037000
[10073.041302] x21: ffff843f66800040 x20: 0000000000000140
[10073.041305] x19: ffff803f62e108c8 x18: 0000000000000007
[10073.041309] x17: 000000000000000e x16: 0000000000000001
[10073.041312] x15: 0000000000000019 x14: 0000000000000033
[10073.041317] x13: 000000000000004c x12: 0000000000000000
[10073.041320] x11: 0000000000001000 x10: 0000000000000010
[10073.041323] x9 : ffff8000004f3a7c x8 : ffff803f69b59120
[10073.041327] x7 : 0000000000000000 x6 : 0000000000000002
[10073.041331] x5 : 0000000000000244 x4 : 00000000000244d9
[10073.041334] x3 : ffff843f653ab918 x2 : 0000000000004074
[10073.041337] x1 : 0000000000000140 x0 : ffff803f62e10e58

===============================================

So add the general dump_stack to show_regs to support showing the stack.

Signed-off-by: Ding Tianhong <dingti...@huawei.com>
---
arch/arm64/kernel/process.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 043d373..60c5c26 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -212,6 +212,7 @@ void show_regs(struct pt_regs * regs)
{
printk("\n");
__show_regs(regs);
+ dump_stack();
}

static void tls_thread_flush(void)
--
1.9.0

[Mark Rutland]

I don't think this is quite right.

I see that x86's show_regs() will dump a kernel stack, but it starts
from the stack described by the regs, not the stack used to call
dump_stack().

Also, for longjmp_break_handler() I think we only want the current
registers, and not the stack.

Thanks,
Mark.

[Kefeng Wang]

I found the same logic exists in arm32.

>
> I see that x86's show_regs() will dump a kernel stack, but it starts
> from the stack described by the regs, not the stack used to call
> dump_stack().
>
> Also, for longjmp_break_handler() I think we only want the current
> registers, and not the stack.

Is there a better way to show the kernel stack? it is not early to address issue
if only show regs. Making a new show_regs() to call dump_mem()/dump_backtrace()/dump_instr()?

Thanks,
Kefeng

>
> Thanks,
> Mark.
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-ar...@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>
> .
>

[Mark Rutland]

First, I think we can make longjmp_break_handler() use __show_regs().

Second, I think we can make show_regs() call dump_backtrace(), passing
the regs down. I believe that should trigger the existing frame
skipping, though we might need some fixups to cater for this particular
case.

Thanks,
Mark.