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Date: Thu, 18 Feb 2016 14:37:09 +0000 From: Russell King - ARM Linux <linux@....linux.org.uk> To: Arnd Bergmann <arnd@...db.de> Cc: linux-arm-kernel@...ts.infradead.org, Ard Biesheuvel <ard.biesheuvel@...aro.org>, Nicolas Pitre <nico@...aro.org>, Jon Medhurst <tixy@...aro.org>, Marc Zyngier <marc.zyngier@....com>, Daniel Thompson <daniel.thompson@...aro.org>, linux-kernel@...r.kernel.org Subject: Re: [PATCH 2/9] ARM: change NR_IPIS to 8 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. -- RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net.
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