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Commit 7974891d authored by Christoph Hellwig's avatar Christoph Hellwig Committed by Thomas Gleixner
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x86: Always use irq stacks 



IRQ stacks provide much better safety against unexpected stack use from
interrupts, at the minimal downside of slightly higher memory usage.
Enable irq stacks also for the default 8k stack on 32-bit kernels to
minimize the problem of stack overflows through interrupt activity.

This is what the 64-bit kernel and various other architectures already do.

Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
LKML-Reference: <20100628121554.GA6605@lst.de>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 5904b3b8

Documentation/x86/x86_64/kernel-stacks

+3 −3
Original line number Diff line number Diff line
@@ -18,9 +18,9 @@ specialized stacks contain no useful data. The main CPU stacks are: 
  Used for external hardware interrupts.  If this is the first external

  hardware interrupt (i.e. not a nested hardware interrupt) then the

  kernel switches from the current task to the interrupt stack.  Like

  the split thread and interrupt stacks on i386 (with CONFIG_4KSTACKS),

  this gives more room for kernel interrupt processing without having

  to increase the size of every per thread stack.

  the split thread and interrupt stacks on i386, this gives more room

  for kernel interrupt processing without having to increase the size

  of every per thread stack.



  The interrupt stack is also used when processing a softirq.

arch/x86/Kconfig.debug

+1 −2
Original line number Diff line number Diff line
@@ -128,8 +128,7 @@ config 4KSTACKS 
	  If you say Y here the kernel will use a 4Kb stacksize for the

	  kernel stack attached to each process/thread. This facilitates

	  running more threads on a system and also reduces the pressure

	  on the VM subsystem for higher order allocations. This option

	  will also use IRQ stacks to compensate for the reduced stackspace.

	  on the VM subsystem for higher order allocations.



config DOUBLEFAULT

	default y

arch/x86/include/asm/irq.h

+5 −7
Original line number Diff line number Diff line
@@ -19,18 +19,16 @@ static inline int irq_canonicalize(int irq) 
# define ARCH_HAS_NMI_WATCHDOG

#endif



#ifdef CONFIG_4KSTACKS

#ifdef CONFIG_X86_32

extern void irq_ctx_init(int cpu);

extern void irq_ctx_exit(int cpu);

# define __ARCH_HAS_DO_SOFTIRQ

#else

# define irq_ctx_init(cpu) do { } while (0)

# define irq_ctx_exit(cpu) do { } while (0)

# ifdef CONFIG_X86_64

#  define __ARCH_HAS_DO_SOFTIRQ

# endif

#endif



#define __ARCH_HAS_DO_SOFTIRQ



#ifdef CONFIG_HOTPLUG_CPU

#include <linux/cpumask.h>

extern void fixup_irqs(void);

arch/x86/kernel/irq_32.c

+0 −6
Original line number Diff line number Diff line
@@ -49,7 +49,6 @@ static inline int check_stack_overflow(void) { return 0; } 
static inline void print_stack_overflow(void) { }

#endif



#ifdef CONFIG_4KSTACKS

/*

 * per-CPU IRQ handling contexts (thread information and stack)

 */
@@ -187,11 +186,6 @@ asmlinkage void do_softirq(void) 
	local_irq_restore(flags);

}



#else

static inline int

execute_on_irq_stack(int overflow, struct irq_desc *desc, int irq) { return 0; }

#endif



bool handle_irq(unsigned irq, struct pt_regs *regs)

{

	struct irq_desc *desc;