From 34a6980c82fb1342e7064844c95aa4cf933e5ecc Mon Sep 17 00:00:00 2001 From: Robin Murphy Date: Thu, 1 Dec 2016 15:55:13 +0000 Subject: [PATCH] arm64: smp: Prevent raw_smp_processor_id() recursion Under CONFIG_DEBUG_PREEMPT=y, this_cpu_ptr() ends up calling back into raw_smp_processor_id(), resulting in some hilariously catastrophic infinite recursion. In the normal case, we have: #define this_cpu_ptr(ptr) raw_cpu_ptr(ptr) and everything is dandy. However for CONFIG_DEBUG_PREEMPT, this_cpu_ptr() is defined in terms of my_cpu_offset, wherein the fun begins: #define my_cpu_offset per_cpu_offset(smp_processor_id()) ... #define smp_processor_id() debug_smp_processor_id() ... notrace unsigned int debug_smp_processor_id(void) { return check_preemption_disabled("smp_processor_id", ""); ... notrace static unsigned int check_preemption_disabled(const char *what1, const char *what2) { int this_cpu = raw_smp_processor_id(); and bang. Use raw_cpu_ptr() directly to avoid that. Fixes: 57c82954e77f ("arm64: make cpu number a percpu variable") Reported-by: Marek Szyprowski Acked-by: Will Deacon Signed-off-by: Robin Murphy Tested-by: Marek Szyprowski Signed-off-by: Catalin Marinas --- arch/arm64/include/asm/smp.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/arch/arm64/include/asm/smp.h b/arch/arm64/include/asm/smp.h index a62db952ffcb..d050d720a1b4 100644 --- a/arch/arm64/include/asm/smp.h +++ b/arch/arm64/include/asm/smp.h @@ -41,8 +41,10 @@ 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. + * And we can't use this_cpu_ptr() either, as that winds up recursing back + * here under CONFIG_DEBUG_PREEMPT=y. */ -#define raw_smp_processor_id() (*this_cpu_ptr(&cpu_number)) +#define raw_smp_processor_id() (*raw_cpu_ptr(&cpu_number)) struct seq_file; -- 2.39.2