[PATCHv3 1/4] Revert "perf/x86: Always store regs->ip in perf_callchain_kernel()"

Jiri Olsa
2025-11-04T21:54:25Z

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 <song@kernel.org>
Signed-off-by: Jiri Olsa <jolsa@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