From 7596abf2e5661d52c4f414f37addeed54e098880 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Wed, 9 Dec 2015 13:58:42 +0000 Subject: [PATCH] arm64: irq: fix walking from irq stack to task stack Running with CONFIG_DEBUG_SPINLOCK=y can trigger a BUG with the new IRQ stack code: BUG: spinlock lockup suspected on CPU#1 This is due to the IRQ_STACK_TO_TASK_STACK macro incorrectly retrieving the task stack pointer stashed at the top of the IRQ stack. Sayeth James: | Yup, this is what is happening. Its an off-by-one due to broken | thinking about how the stack works. My broken thinking was: | | > top ------------ | > | dummy_lr | <- irq_stack_ptr | > ------------ | > | x29 | | > ------------ | > | x19 | <- irq_stack_ptr - 0x10 | > ------------ | > | xzr | | > ------------ | | But the stack-pointer is decreased before use. So it actually looks | like this: | | > ------------ | > | | <- irq_stack_ptr | > top ------------ | > | dummy_lr | | > ------------ | > | x29 | <- irq_stack_ptr - 0x10 | > ------------ | > | x19 | | > ------------ | > | xzr | <- irq_stack_ptr - 0x20 | > ------------ | | The value being used as the original stack is x29, which in all the | tests is sp but without the current frames data, hence there are no | missing frames in the output. | | Jungseok Lee picked it up with a 32bit user space because aarch32 | can't use x29, so it remains 0 forever. The fix he posted is correct. This patch fixes the macro and adds some of this wisdom to a comment, so that the layout of the IRQ stack is well understood. Cc: James Morse Reported-by: Jungseok Lee Signed-off-by: Will Deacon --- arch/arm64/include/asm/irq.h | 20 ++++++++++++++++++-- arch/arm64/kernel/entry.S | 2 +- 2 files changed, 19 insertions(+), 3 deletions(-) diff --git a/arch/arm64/include/asm/irq.h b/arch/arm64/include/asm/irq.h index fa2a8d0e4792..877c7e358384 100644 --- a/arch/arm64/include/asm/irq.h +++ b/arch/arm64/include/asm/irq.h @@ -19,7 +19,23 @@ DECLARE_PER_CPU(unsigned long [IRQ_STACK_SIZE/sizeof(long)], irq_stack); /* * The highest address on the stack, and the first to be used. Used to - * find the dummy-stack frame put down by el?_irq() in entry.S. + * find the dummy-stack frame put down by el?_irq() in entry.S, which + * is structured as follows: + * + * ------------ + * | | <- irq_stack_ptr + * top ------------ + * | elr_el1 | + * ------------ + * | x29 | <- irq_stack_ptr - 0x10 + * ------------ + * | xzr | + * ------------ + * | x19 | <- irq_stack_ptr - 0x20 + * ------------ + * + * where x19 holds a copy of the task stack pointer. + * */ #define IRQ_STACK_PTR(cpu) ((unsigned long)per_cpu(irq_stack, cpu) + IRQ_STACK_START_SP) @@ -27,7 +43,7 @@ DECLARE_PER_CPU(unsigned long [IRQ_STACK_SIZE/sizeof(long)], irq_stack); * The offset from irq_stack_ptr where entry.S will store the original * stack pointer. Used by unwind_frame() and dump_backtrace(). */ -#define IRQ_STACK_TO_TASK_STACK(ptr) *((unsigned long *)(ptr - 0x10)); +#define IRQ_STACK_TO_TASK_STACK(ptr) *((unsigned long *)(ptr - 0x20)); extern void set_handle_irq(void (*handle_irq)(struct pt_regs *)); diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 8f7e737949fe..be7ec544b540 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -199,7 +199,7 @@ alternative_endif /* Add a dummy stack frame */ stp x29, \dummy_lr, [sp, #-16]! // dummy stack frame mov x29, sp - stp xzr, x19, [sp, #-16]! + stp x19, xzr, [sp, #-16]! 9998: .endm