[patch V2 10/13] x86: Select CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK

[Thomas Gleixner]

From: Thomas Gleixner <t...@linutronix.de>

Now that all invocations of irq_exit_rcu() happen on the irq stack, turn on
CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK which causes the core code to invoke
__do_softirq() directly without going through do_softirq_own_stack().

That means do_softirq_own_stack() is only invoked from task context which
means it can't be on the irq stack. Remove the conditional from
run_softirq_on_irqstack_cond() and rename the function accordingly.

Signed-off-by: Thomas Gleixner <t...@linutronix.de>
Reviewed-by: Kees Cook <keesc...@chromium.org>

---
 arch/x86/Kconfig                 |    1 +
 arch/x86/include/asm/irq_stack.h |   19 ++++++++-----------
 arch/x86/kernel/irq_64.c         |    2 +-
 3 files changed, 10 insertions(+), 12 deletions(-)

--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -187,6 +187,7 @@ config X86
        select HAVE_HW_BREAKPOINT
        select HAVE_IDE
        select HAVE_IOREMAP_PROT
+       select HAVE_IRQ_EXIT_ON_IRQ_STACK       if X86_64
        select HAVE_IRQ_TIME_ACCOUNTING
        select HAVE_KERNEL_BZIP2
        select HAVE_KERNEL_GZIP
--- a/arch/x86/include/asm/irq_stack.h
+++ b/arch/x86/include/asm/irq_stack.h
@@ -189,19 +189,16 @@
        "call %P[__func]                                \n"
 
 /*
- * Macro to invoke __do_softirq on the irq stack. Contrary to the above
- * the only check which is necessary is whether the interrupt stack is
- * in use already.
+ * Macro to invoke __do_softirq on the irq stack. This is only called from
+ * task context when bottom halfs are about to be reenabled and soft
+ * interrupts are pending to be processed. The interrupt stack cannot be in
+ * use here.
  */
-#define run_softirq_on_irqstack_cond()                                 \
+#define run_softirq_on_irqstack()                                      \
 {                                                                      \
-       if (__this_cpu_read(hardirq_stack_inuse)) {                     \
-               __do_softirq();                                         \
-       } else {                                                        \
-               __this_cpu_write(hardirq_stack_inuse, true);            \
-               call_on_irqstack(__do_softirq, ASM_CALL_SOFTIRQ);       \
-               __this_cpu_write(hardirq_stack_inuse, false);           \
-       }                                                               \
+       __this_cpu_write(hardirq_stack_inuse, true);                    \
+       call_on_irqstack(__do_softirq, ASM_CALL_SOFTIRQ);               \
+       __this_cpu_write(hardirq_stack_inuse, false);                   \
 }
 
 #else /* CONFIG_X86_64 */
--- a/arch/x86/kernel/irq_64.c
+++ b/arch/x86/kernel/irq_64.c
@@ -76,5 +76,5 @@ int irq_init_percpu_irqstack(unsigned in
 
 void do_softirq_own_stack(void)
 {
-       run_softirq_on_irqstack_cond();
+       run_softirq_on_irqstack();
 }