x86: Fix dumpstack_64 to keep state of "used" variable in loop

Commit 2223f6f6eeaa "x86: Clean up dumpstack_64.c code" moved the used
variable to a local within the loop, but the in_exception_stack()
depended on being non-volatile with the ability to change it.

By always re-initializing the "used" variable to zero, it would cause
the in_exception_stack() to return the same thing each time, and
cause the dump_stack loop to go into an infinite loop.

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 5 deletions

diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c
index 346b1df2412e..74c262a9b9f1 100644
--- a/arch/x86/kernel/dumpstack_64.c
+++ b/arch/x86/kernel/dumpstack_64.c
@@ -115,19 +115,18 @@ enum stack_type {
 };
 
 static enum stack_type
-analyze_stack(int cpu, struct task_struct *task,
-              unsigned long *stack, unsigned long **stack_end, char **id)
+analyze_stack(int cpu, struct task_struct *task, unsigned long *stack,
+              unsigned long **stack_end, unsigned *used, char **id)
 {
         unsigned long *irq_stack;
         unsigned long addr;
-        unsigned used = 0;
 
         addr = ((unsigned long)stack & (~(THREAD_SIZE - 1)));
         if ((unsigned long)task_stack_page(task) == addr)
                 return STACK_IS_NORMAL;
 
         *stack_end = in_exception_stack(cpu, (unsigned long)stack,
-                                         &used, id);
+                                        used, id);
         if (*stack_end)
                 return STACK_IS_EXCEPTION;
 
@@ -158,6 +157,7 @@ void dump_trace(struct task_struct *task, struct pt_regs *regs,
         struct thread_info *tinfo;
         unsigned long *irq_stack;
         unsigned long dummy;
+        unsigned used = 0;
         int graph = 0;
         int done = 0;
 
@@ -186,7 +186,7 @@ void dump_trace(struct task_struct *task, struct pt_regs *regs,
                 enum stack_type stype;
                 char *id;
 
-                stype = analyze_stack(cpu, task, stack, &stack_end, &id);
+                stype = analyze_stack(cpu, task, stack, &stack_end, &used, &id);
 
                 /* Default finish unless specified to continue */
                 done = 1;