[PATCHv2 1/4] Revert "perf/x86: Always store regs->ip in perf_callchain_kernel()"

[Jiri Olsa]

This reverts commit 83f44ae0f8afcc9da659799db8693f74847e66b3.

Currently we store initial stacktrace entry twice for non-HW ot_regs, which
means callers that fail perf_hw_regs(regs) condition in perf_callchain_kernel.

It's easy to reproduce this bpftrace:

  # bpftrace -e 'tracepoint:sched:sched_process_exec { print(kstack()); }'
  Attaching 1 probe...

        bprm_execve+1767
        bprm_execve+1767
        do_execveat_common.isra.0+425
        __x64_sys_execve+56
        do_syscall_64+133
        entry_SYSCALL_64_after_hwframe+118

When perf_callchain_kernel calls unwind_start with first_frame, AFAICS
we do not skip regs->ip, but it's added as part of the unwind process.
Hence reverting the extra perf_callchain_store for non-hw regs leg.

I was not able to bisect this, so I'm not really sure why this was needed
in v5.2 and why it's not working anymore, but I could see double entries
as far as v5.10.

I did the test for both ORC and framepointer unwind with and without the
this fix and except for the initial entry the stacktraces are the same.

Acked-by: Song Liu <s...@kernel.org>
Signed-off-by: Jiri Olsa <jo...@kernel.org>
---
 arch/x86/events/core.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 745caa6c15a3..fa6c47b50989 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2789,13 +2789,13 @@ perf_callchain_kernel(struct perf_callchain_entry_ctx 
*entry, struct pt_regs *re
                return;
        }
 
-       if (perf_callchain_store(entry, regs->ip))
-               return;
-
-       if (perf_hw_regs(regs))
+       if (perf_hw_regs(regs)) {
+               if (perf_callchain_store(entry, regs->ip))
+                       return;
                unwind_start(&state, current, regs, NULL);
-       else
+       } else {
                unwind_start(&state, current, NULL, (void *)regs->sp);
+       }
 
        for (; !unwind_done(&state); unwind_next_frame(&state)) {
                addr = unwind_get_return_address(&state);
-- 
2.51.0