From e333332657f615ac2b55aa35565c4a882018bbe9 Mon Sep 17 00:00:00 2001
From: pengdonglin <pengdonglin@xiaomi.com>
Date: Mon, 12 May 2025 17:42:45 +0800
Subject: [PATCH] ftrace: Fix preemption accounting for stacktrace trigger
command
When using the stacktrace trigger command to trace syscalls, the
preemption count was consistently reported as 1 when the system call
event itself had 0 (".").
For example:
root@ubuntu22-vm:/sys/kernel/tracing/events/syscalls/sys_enter_read
$ echo stacktrace > trigger
$ echo 1 > enable
sshd-416 [002] ..... 232.864910: sys_read(fd: a, buf: 556b1f3221d0, count: 8000)
sshd-416 [002] ...1. 232.864913: <stack trace>
=> ftrace_syscall_enter
=> syscall_trace_enter
=> do_syscall_64
=> entry_SYSCALL_64_after_hwframe
The root cause is that the trace framework disables preemption in __DO_TRACE before
invoking the trigger callback.
Use the tracing_gen_ctx_dec() that will accommodate for the increase of
the preemption count in __DO_TRACE when calling the callback. The result
is the accurate reporting of:
sshd-410 [004] ..... 210.117660: sys_read(fd: 4, buf: 559b725ba130, count: 40000)
sshd-410 [004] ..... 210.117662: <stack trace>
=> ftrace_syscall_enter
=> syscall_trace_enter
=> do_syscall_64
=> entry_SYSCALL_64_after_hwframe
Cc: stable@vger.kernel.org
Fixes: ce33c845b030c ("tracing: Dump stacktrace trigger to the corresponding instance")
Link: https://lore.kernel.org/20250512094246.1167956-1-dolinux.peng@gmail.com
Signed-off-by: pengdonglin <dolinux.peng@gmail.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
kernel/trace/trace_events_trigger.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c
index b66b6d235d91..6e87ae2a1a66 100644
--- a/kernel/trace/trace_events_trigger.c
+++ b/kernel/trace/trace_events_trigger.c
@@ -1560,7 +1560,7 @@ stacktrace_trigger(struct event_trigger_data *data,
struct trace_event_file *file = data->private_data;
if (file)
- __trace_stack(file->tr, tracing_gen_ctx(), STACK_SKIP);
+ __trace_stack(file->tr, tracing_gen_ctx_dec(), STACK_SKIP);
else
trace_dump_stack(STACK_SKIP);
}