x86: Clean up the range of stack overflow checking

The overflow checking of kernel stack checks if the stack
pointer points to the available kernel stack range, which is
derived from the original overflow checking.

It is clear that curbase address is always less than low
boundary of available kernel stack. So, this patch removes the
first condition that checks if the pointer is higher than
curbase.

Signed-off-by: Mitsuo Hayasaka <mitsuo.hayasaka.hu@hitachi.com>
Cc: yrl.pp-manager.tt@hitachi.com
Cc: Randy Dunlap <rdunlap@xenotime.net>
Link: http://lkml.kernel.org/r/20111129060845.11076.40916.stgit@ltc219.sdl.hitachi.co.jp
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: "H. Peter Anvin" <hpa@zytor.com>

diff --git a/arch/x86/kernel/irq_64.c b/arch/x86/kernel/irq_64.c
index 42552b0dce6a95ad51c83faaf8ccfe0b7962bd89..54e2b2b2e250f6f7378d3aab56e84c18e4402108 100644 (file)
--- a/arch/x86/kernel/irq_64.c
+++ b/arch/x86/kernel/irq_64.c
@@ -46,10 +46,9 @@ static inline void stack_overflow_check(struct pt_regs *regs)
        if (user_mode_vm(regs))
                return;
 
-       if (regs->sp >= curbase &&
-           regs->sp <= curbase + THREAD_SIZE &&
-           regs->sp >= curbase + sizeof(struct thread_info) +
-                                 sizeof(struct pt_regs) + 128)
+       if (regs->sp >= curbase + sizeof(struct thread_info) +
+                                 sizeof(struct pt_regs) + 128 &&
+           regs->sp <= curbase + THREAD_SIZE)
                return;
 
        irq_stack_top = (u64)__get_cpu_var(irq_stack_union.irq_stack);