linux_dsm_epyc7002/arch/arm64/include/asm/irq.h
Will Deacon 7596abf2e5 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 <james.morse@arm.com>
Reported-by: Jungseok Lee <jungseoklee85@gmail.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
2015-12-09 13:59:09 +00:00

66 lines
1.6 KiB
C

#ifndef __ASM_IRQ_H
#define __ASM_IRQ_H
#define IRQ_STACK_SIZE THREAD_SIZE
#define IRQ_STACK_START_SP THREAD_START_SP
#ifndef __ASSEMBLER__
#include <linux/percpu.h>
#include <asm-generic/irq.h>
#include <asm/thread_info.h>
#define __ARCH_HAS_DO_SOFTIRQ
struct pt_regs;
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, 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)
/*
* 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 - 0x20));
extern void set_handle_irq(void (*handle_irq)(struct pt_regs *));
static inline int nr_legacy_irqs(void)
{
return 0;
}
static inline bool on_irq_stack(unsigned long sp, int cpu)
{
/* variable names the same as kernel/stacktrace.c */
unsigned long low = (unsigned long)per_cpu(irq_stack, cpu);
unsigned long high = low + IRQ_STACK_START_SP;
return (low <= sp && sp <= high);
}
#endif /* !__ASSEMBLER__ */
#endif