| Message ID | 1480604407-6022-1-git-send-email-m.szyprowski@samsung.com |
|---|---|
| State | New |
| Headers | show |
On Thu, Dec 01, 2016 at 04:00:07PM +0100, Marek Szyprowski wrote: > Direct access to cpu_number entry in per-cpu variables causes boot > failure on Exynos5433, so replace it with this_cpu_read() macro. > This approach is also used on x86_64. Right, but x86 doesn't need to disable preemption in their per-cpu ops afaik, so they don't take the performance hit. Is this failure specific to Exynos5433? > Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com> > --- > This change is needed to get linux-next to boot on Exynos5433, otherwise it > hangs somewhere in early init. There is even no message on the earlycon. > > This issue appeared first on linux-next from 14.11.2016. The tree from > 11.11.2016 is the last one, which boots on Exynos5433. I've tried to > debug a bit this issue, but I ran out of ideas. I suspect the culprit is 57c82954e77f ("arm64: make cpu number a percpu variable"). > > Any comments or suggestions are welcome. > > Best regards > Marek Szyprowski > Samsung R&D Institute Poland > --- > arch/arm64/include/asm/smp.h | 7 +------ > 1 file changed, 1 insertion(+), 6 deletions(-) > > diff --git a/arch/arm64/include/asm/smp.h b/arch/arm64/include/asm/smp.h > index a62db952ffcb..d514383d6219 100644 > --- a/arch/arm64/include/asm/smp.h > +++ b/arch/arm64/include/asm/smp.h > @@ -37,12 +37,7 @@ > > DECLARE_PER_CPU_READ_MOSTLY(int, cpu_number); > > -/* > - * We don't use this_cpu_read(cpu_number) as that has implicit writes to > - * preempt_count, and associated (compiler) barriers, that we'd like to avoid > - * the expense of. If we're preemptible, the value can be stale at use anyway. > - */ > -#define raw_smp_processor_id() (*this_cpu_ptr(&cpu_number)) > +#define raw_smp_processor_id() (this_cpu_read(cpu_number)) I think the issue here is that, in the case of CONFIG_DEBUG_PREEMPT=y, this_cpu_ptr ends up calling back into raw_smp_processor_id() via my_cpu_offset, whereas this_cpu_read always uses __my_cpu_offset and avoids the loop. The right answer is probably to use raw_cpu_ptr instead, and update the comment to explain why. Do you have CONFIG_DEBUG_PREEMPT=y? Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
diff --git a/arch/arm64/include/asm/smp.h b/arch/arm64/include/asm/smp.h index a62db952ffcb..d514383d6219 100644 --- a/arch/arm64/include/asm/smp.h +++ b/arch/arm64/include/asm/smp.h @@ -37,12 +37,7 @@ DECLARE_PER_CPU_READ_MOSTLY(int, cpu_number); -/* - * We don't use this_cpu_read(cpu_number) as that has implicit writes to - * preempt_count, and associated (compiler) barriers, that we'd like to avoid - * the expense of. If we're preemptible, the value can be stale at use anyway. - */ -#define raw_smp_processor_id() (*this_cpu_ptr(&cpu_number)) +#define raw_smp_processor_id() (this_cpu_read(cpu_number)) struct seq_file;
Direct access to cpu_number entry in per-cpu variables causes boot failure on Exynos5433, so replace it with this_cpu_read() macro. This approach is also used on x86_64. Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com> --- This change is needed to get linux-next to boot on Exynos5433, otherwise it hangs somewhere in early init. There is even no message on the earlycon. This issue appeared first on linux-next from 14.11.2016. The tree from 11.11.2016 is the last one, which boots on Exynos5433. I've tried to debug a bit this issue, but I ran out of ideas. Any comments or suggestions are welcome. Best regards Marek Szyprowski Samsung R&D Institute Poland --- arch/arm64/include/asm/smp.h | 7 +------ 1 file changed, 1 insertion(+), 6 deletions(-) -- 1.9.1 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel