Hi Arnd,

On 18/02/16 14:01, Arnd Bergmann wrote:

When function tracing for IPIs is enabled, we get a warning for an
overflow of the ipi_types array with the IPI_CPU_BACKTRACE type
as triggered by raise_nmi():

arch/arm/kernel/smp.c: In function 'raise_nmi':
arch/arm/kernel/smp.c:489:2: error: array subscript is above array bounds [-Werror=array-bounds]
  trace_ipi_raise(target, ipi_types[ipinr]);

This is a correct warning as we actually overflow the array here.
To make the tracing work correctly, this extends the array by one
entry and increases NR_IPI accordingly.

This only works after patch e7273ff49acf ("ARM: 8488/1: Make
IPI_CPU_BACKTRACE a "non-secure" SGI"), which changed the number
assignment from '15' to '8'. If we decide to backport this patch
to stable kernels, we probably need to backport e7273ff49acf
as well.

I may actually have made the bug worse in 89d798b ("ARM: 8487/1: Remove
IPI_CALL_FUNC_SINGLE"), which changed NR_IPI from 8 to 7. It would need
to be backported as well (as otherwise we don't have a free non-secure
IP slot).

As far as I can tell, the problem has existed since the tracepoints
were originally added, but it only triggered a gcc warning with the
later change to NR_IPIS.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: e7273ff49acf ("ARM: 8488/1: Make IPI_CPU_BACKTRACE a "non-secure" SGI")
Fixes: 365ec7b17327 ("ARM: add IPI tracepoints") # v3.17

Acked-by: Marc Zyngier <redacted>

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...