linux-kernel - [PATCH] tracing: fprobe: Fix inifinite recursion using preempt_*

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Message-ID:  <175374642359.1471729.1054175011228386560.stgit@mhiramat.tok.corp.google.com>
Date: Tue, 29 Jul 2025 08:47:03 +0900
From: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
To: Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org
Subject: [PATCH] tracing: fprobe: Fix inifinite recursion using preempt_*_notrace()

From: Masami Hiramatsu (Google) <mhiramat@...nel.org>

Since preempt_count_add/del() are tracable functions, it is not allowed
to use preempt_disable/enable() in ftrace handlers. Without this fix,
probing on `preempt_count_add%return` will cause an infinite recursion
of fprobes.

To fix this problem, use preempt_disable/enable_notrace() in
fprobe_return().

Fixes: 4346ba160409 ("fprobe: Rewrite fprobe on function-graph tracer")
Cc: stable@...r.kernel.org
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
---
 kernel/trace/fprobe.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
index b78fce0982c7..c8034dfc1070 100644
--- a/kernel/trace/fprobe.c
+++ b/kernel/trace/fprobe.c
@@ -352,7 +352,7 @@ static void fprobe_return(struct ftrace_graph_ret *trace,
 	size_words = SIZE_IN_LONG(size);
 	ret_ip = ftrace_regs_get_instruction_pointer(fregs);
 
-	preempt_disable();
+	preempt_disable_notrace();
 
 	curr = 0;
 	while (size_words > curr) {
@@ -368,7 +368,7 @@ static void fprobe_return(struct ftrace_graph_ret *trace,
 		}
 		curr += size;
 	}
-	preempt_enable();
+	preempt_enable_notrace();
 }
 NOKPROBE_SYMBOL(fprobe_return);