x86/dumpstack: Remove 64-byte gap at end of irq stack

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>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Byungchul Park <byungchul.park@lge.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nilay Vaish <nilayvaish@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/14f9281c5475cc44af95945ea7546bff2e3836db.1471535549.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 809eda0..6ef55e8 100644 (file)
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1281,7 +1281,7 @@ 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..066eb5c 100644 (file)
--- 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 7a40e06..d182799 100644 (file)
--- 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) =