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Subject[PATCH v4 29/57] ftrace/x86: implement HAVE_FUNCTION_GRAPH_RET_ADDR_PTR
Date
This allows the use of 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):

Before:
$ 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

After:
$ 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 caused the stack trace to change: it was
offset by 2 frames because the unwinder started with an earlier stack
frame and got out of sync with the ret_stack index.

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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