x86: Eliminate bp argument from the stack tracing routines

The various stack tracing routines take a 'bp' argument in which the
caller is supposed to provide the base pointer to use, or 0 if doesn't
have one. Since bp is garbage whenever CONFIG_FRAME_POINTER is not
defined, this means all callers in principle should either always pass
0, or be conditional on CONFIG_FRAME_POINTER.

However, there are only really three use cases for stack tracing:

(a) Trace the current task, including IRQ stack if any
(b) Trace the current task, but skip IRQ stack
(c) Trace some other task

In all cases, if CONFIG_FRAME_POINTER is not defined, bp should just
be 0.  If it _is_ defined, then

- in case (a) bp should be gotten directly from the CPU's register, so
  the caller should pass NULL for regs,

- in case (b) the caller should should pass the IRQ registers to
  dump_trace(),

- in case (c) bp should be gotten from the top of the task's stack, so
  the caller should pass NULL for regs.

Hence, the bp argument is not necessary because the combination of
task and regs is sufficient to determine an appropriate value for bp.

This patch introduces a new inline function stack_frame(task, regs)
that computes the desired bp. This function is then called from the
two versions of dump_stack().

Signed-off-by: Soren Sandmann <ssp@redhat.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arjan van de Ven <arjan@infradead.org>,
Cc: Frederic Weisbecker <fweisbec@gmail.com>,
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>,
LKML-Reference: <m3oc9rop28.fsf@dhcp-100-3-82.bos.redhat.com>>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

1 files changed, 7 insertions, 17 deletions

diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c
index 6a340485249a..64101335de19 100644
--- a/arch/x86/kernel/dumpstack_64.c
+++ b/arch/x86/kernel/dumpstack_64.c
@@ -139,8 +139,8 @@ fixup_bp_irq_link(unsigned long bp, unsigned long *stack,
  * severe exception (double fault, nmi, stack fault, debug, mce) hardware stack
  */
 
-void dump_trace(struct task_struct *task, struct pt_regs *regs,
-                unsigned long *stack, unsigned long bp,
+void dump_trace(struct task_struct *task,
+                struct pt_regs *regs, unsigned long *stack,
                 const struct stacktrace_ops *ops, void *data)
 {
         const unsigned cpu = get_cpu();
@@ -149,6 +149,7 @@ void dump_trace(struct task_struct *task, struct pt_regs *regs,
         unsigned used = 0;
         struct thread_info *tinfo;
         int graph = 0;
+        unsigned long bp;
 
         if (!task)
                 task = current;
@@ -160,18 +161,7 @@ void dump_trace(struct task_struct *task, struct pt_regs *regs,
                         stack = (unsigned long *)task->thread.sp;
         }
 
-#ifdef CONFIG_FRAME_POINTER
-        if (!bp) {
-                if (task == current) {
-                        /* Grab bp right from our regs */
-                        get_bp(bp);
-                } else {
-                        /* bp is the last reg pushed by switch_to */
-                        bp = *(unsigned long *) task->thread.sp;
-                }
-        }
-#endif
-
+        bp = stack_frame(task, regs);
         /*
          * Print function call entries in all stacks, starting at the
          * current stack address. If the stacks consist of nested
@@ -235,7 +225,7 @@ EXPORT_SYMBOL(dump_trace);
 
 void
 show_stack_log_lvl(struct task_struct *task, struct pt_regs *regs,
-                   unsigned long *sp, unsigned long bp, char *log_lvl)
+                   unsigned long *sp, char *log_lvl)
 {
         unsigned long *irq_stack_end;
         unsigned long *irq_stack;
@@ -279,7 +269,7 @@ show_stack_log_lvl(struct task_struct *task, struct pt_regs *regs,
         preempt_enable();
 
         printk(KERN_CONT "\n");
-        show_trace_log_lvl(task, regs, sp, bp, log_lvl);
+        show_trace_log_lvl(task, regs, sp, log_lvl);
 }
 
 void show_registers(struct pt_regs *regs)
@@ -308,7 +298,7 @@ void show_registers(struct pt_regs *regs)
 
                 printk(KERN_EMERG "Stack:\n");
                 show_stack_log_lvl(NULL, regs, (unsigned long *)sp,
-                                regs->bp, KERN_EMERG);
+                                   KERN_EMERG);
 
                 printk(KERN_EMERG "Code: ");