On Thu, Feb 18, 2016 at 03:01:54PM +0100, 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]);
We really don't want to treat the backtrace IPI as a normal IPI at all -
we want it to invoke the least amount of code possible. Hence this code
which avoids the issue:
if ((unsigned)ipinr < NR_IPI) {
trace_ipi_entry_rcuidle(ipi_types[ipinr]);
__inc_irq_stat(cpu, ipi_irqs[ipinr]);
}
However, what's missing is that the addition of tracing here missed
that CPU_BACKTRACE is not to be traced. The call in raise_nmi()
should have been converted to __smp_cross_call() to avoid the
tracing code.
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