On Fri, Mar 28, 2014 at 03:38:32PM +0800, Dongsheng Wang wrote:

From: Wang Dongsheng <redacted>

If softirq use hardirq stack, we will get kernel painc when a hard irq coming again
during __do_softirq enable local irq to deal with softirq action. So we need to switch
satck into softirq stack when invoke soft irq.

 Task--->
	| Task stack
	|
	Interrput->EXCEPTION->do_IRQ->
	^			     | Hard irq stack
	|			     |
	|			     irq_exit->__do_softirq->local_irq_enable--   -->local_irq_disable
	|									| Hard irq stack
	|									|
	|									Interrupt coming again
	|		There will get a Interrupt nesting			|
	------------------------------------------------------------------------

Trace 1: Trap 900

Kernel stack overflow in process e8152f40, r1=e8e05ec0
CPU: 0 PID: 2399 Comm: image_compress/ Not tainted 3.13.0-rc3-03475-g2e3f85b #432
task: e8152f40 ti: c080a000 task.ti: ef176000
NIP: c05bec04 LR: c0305590 CTR: 00000010
REGS: e8e05e10 TRAP: 0901   Not tainted  (3.13.0-rc3-03475-g2e3f85b)

Could you double check if you got the following patch applied?

commit 1a18a66446f3f289b05b634f18012424d82aa63a
Author: Kevin Hao [off-list ref]
Date:   Fri Jan 17 12:25:28 2014 +0800

    powerpc: Set the correct ksp_limit on ppc32 when switching to irq stack
    
    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.
    
    Cc: stable@vger.kernel.org # 3.12
    Reported-by: Guenter Roeck [off-list ref]
    Tested-by: Guenter Roeck [off-list ref]
    Signed-off-by: Kevin Hao [off-list ref]
    Signed-off-by: Benjamin Herrenschmidt [off-list ref]

Thanks,
Kevin