[PATCH 8/8] x86: remove 64-byte gap at end of irq stack

Josh Poimboeuf
2016-08-19T01:57:53Z

There has been a 64-byte gap at the end of the irq stack for at least 12
years. It predates git history, and I can't find any good reason for
it. Remove it. What's the worst that could happen?

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
arch/x86/kernel/cpu/common.c | 2 +-
arch/x86/kernel/dumpstack_64.c | 9 +++------
arch/x86/kernel/setup_percpu.c | 2 +-
3 files changed, 5 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index d3b91be..ce7a4c1 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1286,7 +1286,7 @@ DEFINE_PER_CPU(struct task_struct *, current_task) ____cacheline_aligned =
EXPORT_PER_CPU_SYMBOL(current_task);

DEFINE_PER_CPU(char *, irq_stack_ptr) =
- init_per_cpu_var(irq_stack_union.irq_stack) + IRQ_STACK_SIZE - 64;
+ init_per_cpu_var(irq_stack_union.irq_stack) + IRQ_STACK_SIZE;

DEFINE_PER_CPU(unsigned int, irq_count) __visible = -1;

diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c
index daf9f63..066eb5c7 100644
--- a/arch/x86/kernel/dumpstack_64.c
+++ b/arch/x86/kernel/dumpstack_64.c
@@ -103,9 +103,6 @@ in_irq_stack(unsigned long *stack, unsigned long *irq_stack,
return (stack >= irq_stack && stack < irq_stack_end);
}

-static const unsigned long irq_stack_size =
- (IRQ_STACK_SIZE - 64) / sizeof(unsigned long);
-
enum stack_type {
STACK_IS_UNKNOWN,
STACK_IS_NORMAL,
@@ -133,7 +130,7 @@ analyze_stack(int cpu, struct task_struct *task, unsigned long *stack,
return STACK_IS_NORMAL;

*stack_end = irq_stack;
- irq_stack = irq_stack - irq_stack_size;
+ irq_stack -= (IRQ_STACK_SIZE / sizeof(long));

if (in_irq_stack(stack, irq_stack, *stack_end))
return STACK_IS_IRQ;
@@ -256,8 +253,8 @@ show_stack_log_lvl(struct task_struct *task, struct pt_regs *regs,
preempt_disable();
cpu = smp_processor_id();

- irq_stack_end = (unsigned long *)(per_cpu(irq_stack_ptr, cpu));
- irq_stack = (unsigned long *)(per_cpu(irq_stack_ptr, cpu) - IRQ_STACK_SIZE);
+ irq_stack_end = (unsigned long *)(per_cpu(irq_stack_ptr, cpu));
+ irq_stack = irq_stack_end - (IRQ_STACK_SIZE / sizeof(long));

/*
* Debugging aid: "show_stack(NULL, NULL);" prints the
diff --git a/arch/x86/kernel/setup_percpu.c b/arch/x86/kernel/setup_percpu.c
index 1d5c794..2bbd27f 100644
--- a/arch/x86/kernel/setup_percpu.c
+++ b/arch/x86/kernel/setup_percpu.c
@@ -246,7 +246,7 @@ void __init setup_per_cpu_areas(void)
#ifdef CONFIG_X86_64
per_cpu(irq_stack_ptr, cpu) =
per_cpu(irq_stack_union.irq_stack, cpu) +
- IRQ_STACK_SIZE - 64;
+ IRQ_STACK_SIZE;
#endif
#ifdef CONFIG_NUMA
per_cpu(x86_cpu_to_node_map, cpu) =
--
2.7.4