linux-kernel - kernel/trace/fgraph.c:834 __ftrace_return_to_handler() error: we previously assumed 'fregs' could be null (see line 830)

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Message-ID: <202512131657.JQUt5fXQ-lkp@intel.com>
Date: Fri, 2 Jan 2026 17:49:39 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: oe-kbuild@...ts.linux.dev,
	"Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc: lkp@...el.com, oe-kbuild-all@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	"Steven Rostedt (Google)" <rostedt@...dmis.org>
Subject: kernel/trace/fgraph.c:834 __ftrace_return_to_handler() error: we
 previously assumed 'fregs' could be null (see line 830)

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   a919610db43b34621d0c3b333e12db9002caf5da
commit: 2ca8c112c9676e2394d76760db78ffddf21d93b5 fgraph: Pass ftrace_regs to retfunc
config: arm64-randconfig-r073-20251212 (https://download.01.org/0day-ci/archive/20251213/202512131657.JQUt5fXQ-lkp@intel.com/config)
compiler: clang version 22.0.0git (https://github.com/llvm/llvm-project 1335a05ab8bc8339ce24be3a9da89d8c3f4e0571)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@...el.com>
| Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
| Closes: https://lore.kernel.org/r/202512131657.JQUt5fXQ-lkp@intel.com/

smatch warnings:
kernel/trace/fgraph.c:834 __ftrace_return_to_handler() error: we previously assumed 'fregs' could be null (see line 830)

vim +/fregs +834 kernel/trace/fgraph.c

a3ed4157b7d898 Masami Hiramatsu (Google  2024-12-26  810) static inline unsigned long
a3ed4157b7d898 Masami Hiramatsu (Google  2024-12-26  811) __ftrace_return_to_handler(struct ftrace_regs *fregs, unsigned long frame_pointer)
d864a3ca883095 Steven Rostedt (VMware    2018-11-12  812) {
7aa1eaef9f4282 Steven Rostedt (VMware    2024-06-03  813) 	struct ftrace_ret_stack *ret_stack;
d864a3ca883095 Steven Rostedt (VMware    2018-11-12  814) 	struct ftrace_graph_ret trace;
7aa1eaef9f4282 Steven Rostedt (VMware    2024-06-03  815) 	unsigned long bitmap;
d864a3ca883095 Steven Rostedt (VMware    2018-11-12  816) 	unsigned long ret;
7aa1eaef9f4282 Steven Rostedt (VMware    2024-06-03  817) 	int offset;
7aa1eaef9f4282 Steven Rostedt (VMware    2024-06-03  818) 	int i;
7aa1eaef9f4282 Steven Rostedt (VMware    2024-06-03  819) 
7aa1eaef9f4282 Steven Rostedt (VMware    2024-06-03  820) 	ret_stack = ftrace_pop_return_trace(&trace, &ret, frame_pointer, &offset);
7aa1eaef9f4282 Steven Rostedt (VMware    2024-06-03  821) 
7aa1eaef9f4282 Steven Rostedt (VMware    2024-06-03  822) 	if (unlikely(!ret_stack)) {
7aa1eaef9f4282 Steven Rostedt (VMware    2024-06-03  823) 		ftrace_graph_stop();
7aa1eaef9f4282 Steven Rostedt (VMware    2024-06-03  824) 		WARN_ON(1);
7aa1eaef9f4282 Steven Rostedt (VMware    2024-06-03  825) 		/* Might as well panic. What else to do? */
7aa1eaef9f4282 Steven Rostedt (VMware    2024-06-03  826) 		return (unsigned long)panic;
7aa1eaef9f4282 Steven Rostedt (VMware    2024-06-03  827) 	}
d864a3ca883095 Steven Rostedt (VMware    2018-11-12  828) 
7aa1eaef9f4282 Steven Rostedt (VMware    2024-06-03  829) 	trace.rettime = trace_clock_local();
2ca8c112c9676e Masami Hiramatsu (Google  2024-12-26 @830) 	if (fregs)

It's strange that Smatch is only now complaining about something which
is from 2024...  This line assumes "freqs" can be NULL.

2ca8c112c9676e Masami Hiramatsu (Google  2024-12-26  831) 		ftrace_regs_set_instruction_pointer(fregs, ret);
2ca8c112c9676e Masami Hiramatsu (Google  2024-12-26  832) 
a1be9ccc57f07d Donglin Peng              2023-04-08  833  #ifdef CONFIG_FUNCTION_GRAPH_RETVAL
a3ed4157b7d898 Masami Hiramatsu (Google  2024-12-26 @834) 	trace.retval = ftrace_regs_get_return_value(fregs);
                                                                                                            ^^^^^
Unchecked dereference.

a1be9ccc57f07d Donglin Peng              2023-04-08  835  #endif
7aa1eaef9f4282 Steven Rostedt (VMware    2024-06-03  836) 
7aa1eaef9f4282 Steven Rostedt (VMware    2024-06-03  837) 	bitmap = get_bitmap_bits(current, offset);
420e1354bcb6f0 Steven Rostedt (Google    2024-06-03  838) 

-- 
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https://github.com/intel/lkp-tests/wiki