ftrace: Fix preemption accounting for stacktrace filter command

commit 11aff32439df6ca5b3b891b43032faf88f4a6a29 upstream.

The preemption count of the stacktrace filter command to trace ksys_read
is consistently incorrect:

$ echo ksys_read:stacktrace > set_ftrace_filter

   <...>-453     [004] ...1.    38.308956: <stack trace>
=> ksys_read
=> do_syscall_64
=> entry_SYSCALL_64_after_hwframe

The root cause is that the trace framework disables preemption when
invoking the filter command callback in function_trace_probe_call:

   preempt_disable_notrace();
   probe_ops->func(ip, parent_ip, probe_opsbe->tr, probe_ops, probe->data);
   preempt_enable_notrace();

Use tracing_gen_ctx_dec() to account for the preempt_disable_notrace(),
which will output the correct preemption count:

$ echo ksys_read:stacktrace > set_ftrace_filter

   <...>-410     [006] .....    31.420396: <stack trace>
=> ksys_read
=> do_syscall_64
=> entry_SYSCALL_64_after_hwframe

Cc: stable@vger.kernel.org
Fixes: 36590c50b2d07 ("tracing: Merge irqflags + preempt counter.")
Link: https://lore.kernel.org/20250512094246.1167956-2-dolinux.peng@gmail.com
Signed-off-by: pengdonglin <dolinux.peng@gmail.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/trace/trace_functions.c b/kernel/trace/trace_functions.c
index 69e92c7359fb9a5a81b0ed9cf4321558794f4d27..44ae51d1dc45d8d01cc8e8f938ee23b7149bb380 100644 (file)
--- a/kernel/trace/trace_functions.c
+++ b/kernel/trace/trace_functions.c
@@ -561,11 +561,7 @@ ftrace_traceoff(unsigned long ip, unsigned long parent_ip,
 
 static __always_inline void trace_stack(struct trace_array *tr)
 {
-       unsigned int trace_ctx;
-
-       trace_ctx = tracing_gen_ctx();
-
-       __trace_stack(tr, trace_ctx, FTRACE_STACK_SKIP);
+       __trace_stack(tr, tracing_gen_ctx_dec(), FTRACE_STACK_SKIP);
 }
 
 static void