linux-kernel - Re: [PATCH v4 2/4] tracing: Make the backup instance non-reusable

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Message-ID: <202601201531.ng4kqZhn-lkp@intel.com>
Date: Tue, 20 Jan 2026 16:17:05 +0800
From: kernel test robot <lkp@...el.com>
To: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>
Cc: oe-kbuild-all@...ts.linux.dev, Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/4] tracing: Make the backup instance non-reusable

Hi Masami,

kernel test robot noticed the following build warnings:

[auto build test WARNING on trace/for-next]
[also build test WARNING on linus/master v6.19-rc6 next-20260119]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Masami-Hiramatsu-Google/tracing-Reset-last_boot_info-if-ring-buffer-is-reset/20260120-091429
base:   https://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace for-next
patch link:    https://lore.kernel.org/r/176887137556.578403.17994205756247311821.stgit%40mhiramat.tok.corp.google.com
patch subject: [PATCH v4 2/4] tracing: Make the backup instance non-reusable
config: arc-defconfig (https://download.01.org/0day-ci/archive/20260120/202601201531.ng4kqZhn-lkp@intel.com/config)
compiler: arc-linux-gcc (GCC) 15.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260120/202601201531.ng4kqZhn-lkp@intel.com/reproduce)

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>
| Closes: https://lore.kernel.org/oe-kbuild-all/202601201531.ng4kqZhn-lkp@intel.com/

All warnings (new ones prefixed by >>):

   kernel/trace/trace.c: In function 'tracing_init_tracefs_percpu':
>> kernel/trace/trace.c:9398:17: warning: variable 'writable_mode' set but not used [-Wunused-but-set-variable]
    9398 |         umode_t writable_mode = TRACE_MODE_WRITE;
         |                 ^~~~~~~~~~~~~


vim +/writable_mode +9398 kernel/trace/trace.c

  9393	
  9394	static void
  9395	tracing_init_tracefs_percpu(struct trace_array *tr, long cpu)
  9396	{
  9397		struct dentry *d_percpu = tracing_dentry_percpu(tr, cpu);
> 9398		umode_t writable_mode = TRACE_MODE_WRITE;
  9399		struct dentry *d_cpu;
  9400		char cpu_dir[30]; /* 30 characters should be more than enough */
  9401	
  9402		if (!d_percpu)
  9403			return;
  9404	
  9405		if (trace_array_is_readonly(tr))
  9406			writable_mode = TRACE_MODE_READ;
  9407	
  9408		snprintf(cpu_dir, 30, "cpu%ld", cpu);
  9409		d_cpu = tracefs_create_dir(cpu_dir, d_percpu);
  9410		if (!d_cpu) {
  9411			pr_warn("Could not create tracefs '%s' entry\n", cpu_dir);
  9412			return;
  9413		}
  9414	
  9415		/* per cpu trace_pipe */
  9416		trace_create_cpu_file("trace_pipe", TRACE_MODE_READ, d_cpu,
  9417					tr, cpu, &tracing_pipe_fops);
  9418	
  9419		/* per cpu trace */
  9420		trace_create_cpu_file("trace", TRACE_MODE_WRITE, d_cpu,
  9421					tr, cpu, &tracing_fops);
  9422	
  9423		trace_create_cpu_file("trace_pipe_raw", TRACE_MODE_READ, d_cpu,
  9424					tr, cpu, &tracing_buffers_fops);
  9425	
  9426		trace_create_cpu_file("stats", TRACE_MODE_READ, d_cpu,
  9427					tr, cpu, &tracing_stats_fops);
  9428	
  9429		trace_create_cpu_file("buffer_size_kb", TRACE_MODE_READ, d_cpu,
  9430					tr, cpu, &tracing_entries_fops);
  9431	
  9432		if (tr->range_addr_start)
  9433			trace_create_cpu_file("buffer_meta", TRACE_MODE_READ, d_cpu,
  9434					      tr, cpu, &tracing_buffer_meta_fops);
  9435	#ifdef CONFIG_TRACER_SNAPSHOT
  9436		if (!tr->range_addr_start) {
  9437			trace_create_cpu_file("snapshot", TRACE_MODE_WRITE, d_cpu,
  9438					      tr, cpu, &snapshot_fops);
  9439	
  9440			trace_create_cpu_file("snapshot_raw", TRACE_MODE_READ, d_cpu,
  9441					      tr, cpu, &snapshot_raw_fops);
  9442		}
  9443	#endif
  9444	}
  9445	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki