2 files changed, 18 insertions, 2 deletions

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index caa404556b9c..266e4649b1da 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1093,11 +1093,13 @@ unsigned long kernel_eflags;
 DEFINE_PER_CPU(struct orig_ist, orig_ist);
 
 static DEFINE_PER_CPU(unsigned long, debug_stack_addr);
+DEFINE_PER_CPU(int, debug_stack_usage);
 
 int is_debug_stack(unsigned long addr)
 {
-        return addr <= __get_cpu_var(debug_stack_addr) &&
-                addr > (__get_cpu_var(debug_stack_addr) - DEBUG_STKSZ);
+        return __get_cpu_var(debug_stack_usage) ||
+                (addr <= __get_cpu_var(debug_stack_addr) &&
+                 addr > (__get_cpu_var(debug_stack_addr) - DEBUG_STKSZ));
 }
 
 void debug_stack_set_zero(void)
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index a93c5cabc36a..0072b38e3ea1 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -316,9 +316,15 @@ dotraplinkage void __kprobes do_int3(struct pt_regs *regs, long error_code)
                 return;
 #endif
 
+        /*
+         * Let others (NMI) know that the debug stack is in use
+         * as we may switch to the interrupt stack.
+         */
+        debug_stack_usage_inc();
         preempt_conditional_sti(regs);
         do_trap(3, SIGTRAP, "int3", regs, error_code, NULL);
         preempt_conditional_cli(regs);
+        debug_stack_usage_dec();
 }
 
 #ifdef CONFIG_X86_64
@@ -411,6 +417,12 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code)
                                                         SIGTRAP) == NOTIFY_STOP)
                 return;
 
+        /*
+         * Let others (NMI) know that the debug stack is in use
+         * as we may switch to the interrupt stack.
+         */
+        debug_stack_usage_inc();
+
         /* It's safe to allow irq's after DR6 has been saved */
         preempt_conditional_sti(regs);
 
@@ -418,6 +430,7 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code)
                 handle_vm86_trap((struct kernel_vm86_regs *) regs,
                                 error_code, 1);
                 preempt_conditional_cli(regs);
+                debug_stack_usage_dec();
                 return;
         }
 
@@ -437,6 +450,7 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code)
         if (tsk->thread.debugreg6 & (DR_STEP | DR_TRAP_BITS) || user_icebp)
                 send_sigtrap(tsk, regs, error_code, si_code);
         preempt_conditional_cli(regs);
+        debug_stack_usage_dec();
 
         return;
 }