[PATCH] powerpc: set the correct ksp_limit on ppc32 when switching to irq stack

[Benjamin Herrenschmidt]

On Tue, 2014-01-21 at 08:14 -0800, Guenter Roeck wrote:
> On Fri, Jan 17, 2014 at 12:25:28PM +0800, Kevin Hao wrote:
> > Guenter Roeck has got the following call trace on a p2020 board:
> >   Kernel stack overflow in process eb3e5a00, r1=eb79df90
> >   CPU: 0 PID: 2838 Comm: ssh Not tainted 3.13.0-rc8-juniper-00146-g19eca00 #4
> >   task: eb3e5a00 ti: c0616000 task.ti: ef440000
> >   NIP: c003a420 LR: c003a410 CTR: c0017518
> >   REGS: eb79dee0 TRAP: 0901   Not tainted (3.13.0-rc8-juniper-00146-g19eca00)
> >   MSR: 00029000 <CE,EE,ME>  CR: 24008444  XER: 00000000
> >   GPR00: c003a410 eb79df90 eb3e5a00 00000000 eb05d900 00000001 65d87646 00000000
> >   GPR08: 00000000 020b8000 00000000 00000000 44008442
> >   NIP [c003a420] __do_softirq+0x94/0x1ec
> >   LR [c003a410] __do_softirq+0x84/0x1ec
> >   Call Trace:
> >   [eb79df90] [c003a410] __do_softirq+0x84/0x1ec (unreliable)
> >   [eb79dfe0] [c003a970] irq_exit+0xbc/0xc8
> >   [eb79dff0] [c000cc1c] call_do_irq+0x24/0x3c
> >   [ef441f20] [c00046a8] do_IRQ+0x8c/0xf8
> >   [ef441f40] [c000e7f4] ret_from_except+0x0/0x18
> >   --- Exception: 501 at 0xfcda524
> >       LR = 0x10024900
> >   Instruction dump:
> >   7c781b78 3b40000a 3a73b040 543c0024 3a800000 3b3913a0 7ef5bb78 48201bf9
> >   5463103a 7d3b182e 7e89b92e 7c008146 <3ba00000> 7e7e9b78 48000014 57fff87f
> >   Kernel panic - not syncing: kernel stack overflow
> >   CPU: 0 PID: 2838 Comm: ssh Not tainted 3.13.0-rc8-juniper-00146-g19eca00 #4
> >   Call Trace:
> > 
> > The reason is that we have used the wrong register to calculate the
> > ksp_limit in commit cbc9565ee826 (powerpc: Remove ksp_limit on ppc64).
> > Just fix it.
> > 
> > As suggested by Benjamin Herrenschmidt, also add the C prototype of the
> > function in the comment in order to avoid such kind of errors in the
> > future.
> > 
> Was this patch accepted, or are there any problems with it ?
> I didn't see any comments, and it still isn't upstream nor in linux-next.

It will be merged when I come back from vacation. It was too late for
3.13 so I'll send it to Linus next week and will CC -stable.

Cheers,
Ben.