[PATCH] powerpc/64: Initialise thread_info for emergency stacks

[Abdul Haleem]

On Tue, 2017-06-20 at 23:58 +1000, Nicholas Piggin wrote:
> Emergency stacks have their thread_info mostly uninitialised, which in
> particular means garbage preempt_count values.
> 
> Emergency stack code runs with interrupts disabled entirely, and is
> used very rarely, so this has been unnoticed so far. It was found by a
> proposed new powerpc watchdog that takes a soft-NMI directly from the
> masked_interrupt handler and using the emergency stack. That crashed at
> BUG_ON(in_nmi()) in nmi_enter(). preempt_count()s were found to be
> garbage.
> 
> Reported-by: Abdul Haleem <abdhalee at linux.vnet.ibm.com>
> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
> ---
> 
> FYI, this bug looks to be breaking linux-next on some powerpc
> boxes due to interaction with a proposed new powerpc watchdog
> driver Andrew has in his tree:
> 
> http://marc.info/?l=linuxppc-embedded&m=149794320519941&w=2
> 
>  arch/powerpc/include/asm/thread_info.h | 19 +++++++++++++++++++
>  arch/powerpc/kernel/setup_64.c         |  6 +++---
>  2 files changed, 22 insertions(+), 3 deletions(-)

Hi Nicholas,

Thanks for the patch, Verified on next-20170621 and PowerPC bare-metal
boots fine with your patch

Tested-by: Abdul Haleem <abdhalee at linux.vnet.ibm.com>

Thanks for all your support.

-- 
Regard's

Abdul Haleem
IBM Linux Technology Centre