From: pengdonglin pengdonglin@xiaomi.com
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); }