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[PATCH 6/8] ftrace/x86: implement HAVE_FUNCTION_GRAPH_RET_ADDR_PTR

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Use the more reliable version of ftrace_graph_ret_addr() so we no longer
have to worry about the unwinder getting out of sync with the function
graph ret_stack index, which can happen if the unwinder skips any frames
before calling ftrace_graph_ret_addr().

This fixes this issue (and several others like it):

  $ cat /proc/self/stack
  [<ffffffff810489a2>] save_stack_trace_tsk+0x22/0x40
  [<ffffffff81311a89>] proc_pid_stack+0xb9/0x110
  [<ffffffff813127c4>] proc_single_show+0x54/0x80
  [<ffffffff812be088>] seq_read+0x108/0x3e0
  [<ffffffff812923d7>] __vfs_read+0x37/0x140
  [<ffffffff812929d9>] vfs_read+0x99/0x140
  [<ffffffff81293f28>] SyS_read+0x58/0xc0
  [<ffffffff818af97c>] entry_SYSCALL_64_fastpath+0x1f/0xbd
  [<ffffffffffffffff>] 0xffffffffffffffff

  $ echo function_graph > /sys/kernel/debug/tracing/current_tracer

  $ cat /proc/self/stack
  [<ffffffff818b2428>] return_to_handler+0x0/0x27
  [<ffffffff810394cc>] print_context_stack+0xfc/0x100
  [<ffffffff818b2428>] return_to_handler+0x0/0x27
  [<ffffffff8103891b>] dump_trace+0x12b/0x350
  [<ffffffff818b2428>] return_to_handler+0x0/0x27
  [<ffffffff810489a2>] save_stack_trace_tsk+0x22/0x40
  [<ffffffff818b2428>] return_to_handler+0x0/0x27
  [<ffffffff81311a89>] proc_pid_stack+0xb9/0x110
  [<ffffffff818b2428>] return_to_handler+0x0/0x27
  [<ffffffff813127c4>] proc_single_show+0x54/0x80
  [<ffffffff818b2428>] return_to_handler+0x0/0x27
  [<ffffffff812be088>] seq_read+0x108/0x3e0
  [<ffffffff818b2428>] return_to_handler+0x0/0x27
  [<ffffffff812923d7>] __vfs_read+0x37/0x140
  [<ffffffff818b2428>] return_to_handler+0x0/0x27
  [<ffffffff812929d9>] vfs_read+0x99/0x140
  [<ffffffffffffffff>] 0xffffffffffffffff

Enabling function graph tracing causes the stack trace to change in two
ways:

First, the real call addresses are confusingly interspersed with
'return_to_handler' addresses.  This issue will be fixed by the next
patch.

Second, the stack trace is offset by two frames, because the unwinder
skipped the first two frames and got out of sync with the ret_stack
index.  This patch fixes this issue.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
 arch/x86/include/asm/ftrace.h | 2 ++
 arch/x86/kernel/ftrace.c      | 2 +-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h
index 37f67cb..eccd0ac 100644
--- a/arch/x86/include/asm/ftrace.h
+++ b/arch/x86/include/asm/ftrace.h
@@ -14,6 +14,8 @@
 #define ARCH_SUPPORTS_FTRACE_OPS 1
 #endif
 
+#define HAVE_FUNCTION_GRAPH_RET_ADDR_PTR
+
 #ifndef __ASSEMBLY__
 extern void mcount(void);
 extern atomic_t modifying_ftrace_code;
diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index ae3b1fb..8639bb2 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -1029,7 +1029,7 @@ void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent,
 	}
 
 	if (ftrace_push_return_trace(old, self_addr, &trace.depth,
-				     frame_pointer, NULL) == -EBUSY) {
+				     frame_pointer, parent) == -EBUSY) {
 		*parent = old;
 		return;
 	}
-- 
2.7.4

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[PATCH 0/8] ftrace/x86: function_graph stack dump fixes Josh Poimboeuf <jpoimboe@redhat.com> - 2016-08-19 14:00 +0200
  [PATCH 5/8] x86/dumpstack/ftrace: convert dump_trace() callbacks to use ftrace_graph_ret_addr() Josh Poimboeuf <jpoimboe@redhat.com> - 2016-08-19 14:00 +0200
    [tip:x86/asm] x86/dumpstack/ftrace: Convert dump_trace() callbacks  to use ftrace_graph_ret_addr() tip-bot for Josh Poimboeuf <tipbot@zytor.com> - 2016-08-24 15:50 +0200
  [PATCH 1/8] ftrace: remove CONFIG_HAVE_FUNCTION_GRAPH_FP_TEST from config Josh Poimboeuf <jpoimboe@redhat.com> - 2016-08-19 14:00 +0200
    [tip:x86/asm] ftrace: Remove CONFIG_HAVE_FUNCTION_GRAPH_FP_TEST  from config tip-bot for Josh Poimboeuf <tipbot@zytor.com> - 2016-08-24 15:10 +0200
  [PATCH 7/8] x86/dumpstack/ftrace: mark function graph handler function as unreliable Josh Poimboeuf <jpoimboe@redhat.com> - 2016-08-19 14:00 +0200
    [tip:x86/asm] x86/dumpstack/ftrace: Mark function graph handler  function as unreliable tip-bot for Josh Poimboeuf <tipbot@zytor.com> - 2016-08-24 15:50 +0200
  [PATCH 8/8] x86/dumpstack/ftrace: don't print unreliable addresses in print_context_stack_bp() Josh Poimboeuf <jpoimboe@redhat.com> - 2016-08-19 14:00 +0200
    [tip:x86/asm] x86/dumpstack/ftrace: Don't print unreliable  addresses in print_context_stack_bp() tip-bot for Josh Poimboeuf <tipbot@zytor.com> - 2016-08-24 15:50 +0200
  [PATCH 2/8] ftrace: only allocate the ret_stack 'fp' field when needed Josh Poimboeuf <jpoimboe@redhat.com> - 2016-08-19 14:00 +0200
    [tip:x86/asm] ftrace: Only allocate the ret_stack 'fp' field when  needed tip-bot for Josh Poimboeuf <tipbot@zytor.com> - 2016-08-24 15:10 +0200
  [PATCH 6/8] ftrace/x86: implement HAVE_FUNCTION_GRAPH_RET_ADDR_PTR Josh Poimboeuf <jpoimboe@redhat.com> - 2016-08-19 14:00 +0200
    [tip:x86/asm] ftrace/x86: Implement  HAVE_FUNCTION_GRAPH_RET_ADDR_PTR tip-bot for Josh Poimboeuf <tipbot@zytor.com> - 2016-08-24 15:10 +0200
  [PATCH 4/8] ftrace: add ftrace_graph_ret_addr() stack unwinding helpers Josh Poimboeuf <jpoimboe@redhat.com> - 2016-08-19 14:00 +0200
    [tip:x86/asm] ftrace: Add ftrace_graph_ret_addr() stack unwinding  helpers tip-bot for Josh Poimboeuf <tipbot@zytor.com> - 2016-08-24 15:10 +0200
  Re: [PATCH 0/8] ftrace/x86: function_graph stack dump fixes Steven Rostedt <rostedt@goodmis.org> - 2016-08-23 16:30 +0200
    Re: [PATCH 0/8] ftrace/x86: function_graph stack dump fixes Ingo Molnar <mingo@kernel.org> - 2016-08-24 12:20 +0200

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