linux-kernel - Re: [PATCH v2 07/11] kcov: add trace and trace_size to struct kcov

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Message-ID: <202506271946.HACEE9U0-lkp@intel.com>
Date: Fri, 27 Jun 2025 20:34:24 +0800
From: kernel test robot <lkp@...el.com>
To: Alexander Potapenko <glider@...gle.com>
Cc: llvm@...ts.linux.dev, oe-kbuild-all@...ts.linux.dev,
	quic_jiangenj@...cinc.com, linux-kernel@...r.kernel.org,
	kasan-dev@...glegroups.com, Aleksandr Nogikh <nogikh@...gle.com>,
	Andrey Konovalov <andreyknvl@...il.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Dmitry Vyukov <dvyukov@...gle.com>, Ingo Molnar <mingo@...hat.com>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Marco Elver <elver@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2 07/11] kcov: add trace and trace_size to struct
 kcov_state

Hi Alexander,

kernel test robot noticed the following build warnings:

[auto build test WARNING on tip/x86/core]
[cannot apply to akpm-mm/mm-everything tip/sched/core arnd-asm-generic/master akpm-mm/mm-nonmm-unstable masahiroy-kbuild/for-next masahiroy-kbuild/fixes shuah-kselftest/next shuah-kselftest/fixes linus/master mcgrof/modules-next v6.16-rc3 next-20250627]
[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/Alexander-Potapenko/x86-kcov-disable-instrumentation-of-arch-x86-kernel-tsc-c/20250626-214703
base:   tip/x86/core
patch link:    https://lore.kernel.org/r/20250626134158.3385080-8-glider%40google.com
patch subject: [PATCH v2 07/11] kcov: add trace and trace_size to struct kcov_state
config: x86_64-buildonly-randconfig-004-20250627 (https://download.01.org/0day-ci/archive/20250627/202506271946.HACEE9U0-lkp@intel.com/config)
compiler: clang version 20.1.7 (https://github.com/llvm/llvm-project 6146a88f60492b520a36f8f8f3231e15f3cc6082)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250627/202506271946.HACEE9U0-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/202506271946.HACEE9U0-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> kernel/kcov.c:1013:15: warning: variable 'trace' set but not used [-Wunused-but-set-variable]
    1013 |         void *area, *trace;
         |                      ^
>> kernel/kcov.c:1014:21: warning: variable 'trace_size' set but not used [-Wunused-but-set-variable]
    1014 |         unsigned int size, trace_size;
         |                            ^
   2 warnings generated.


vim +/trace +1013 kernel/kcov.c

  1006	
  1007	/* See the comment before kcov_remote_start() for usage details. */
  1008	void kcov_remote_stop(void)
  1009	{
  1010		struct task_struct *t = current;
  1011		struct kcov *kcov;
  1012		unsigned int mode;
> 1013		void *area, *trace;
> 1014		unsigned int size, trace_size;
  1015		int sequence;
  1016		unsigned long flags;
  1017	
  1018		if (!in_task() && !in_softirq_really())
  1019			return;
  1020	
  1021		local_lock_irqsave(&kcov_percpu_data.lock, flags);
  1022	
  1023		mode = READ_ONCE(t->kcov_mode);
  1024		barrier();
  1025		if (!kcov_mode_enabled(mode)) {
  1026			local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
  1027			return;
  1028		}
  1029		/*
  1030		 * When in softirq, check if the corresponding kcov_remote_start()
  1031		 * actually found the remote handle and started collecting coverage.
  1032		 */
  1033		if (in_serving_softirq() && !t->kcov_softirq) {
  1034			local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
  1035			return;
  1036		}
  1037		/* Make sure that kcov_softirq is only set when in softirq. */
  1038		if (WARN_ON(!in_serving_softirq() && t->kcov_softirq)) {
  1039			local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
  1040			return;
  1041		}
  1042	
  1043		kcov = t->kcov;
  1044		area = t->kcov_state.area;
  1045		size = t->kcov_state.size;
  1046		trace = t->kcov_state.trace;
  1047		trace_size = t->kcov_state.trace_size;
  1048		sequence = t->kcov_state.sequence;
  1049	
  1050		kcov_stop(t);
  1051		if (in_serving_softirq()) {
  1052			t->kcov_softirq = 0;
  1053			kcov_remote_softirq_stop(t);
  1054		}
  1055	
  1056		spin_lock(&kcov->lock);
  1057		/*
  1058		 * KCOV_DISABLE could have been called between kcov_remote_start()
  1059		 * and kcov_remote_stop(), hence the sequence check.
  1060		 */
  1061		if (sequence == kcov->state.sequence && kcov->remote)
  1062			kcov_move_area(kcov->mode, kcov->state.area, kcov->state.size,
  1063				       area);
  1064		spin_unlock(&kcov->lock);
  1065	
  1066		if (in_task()) {
  1067			spin_lock(&kcov_remote_lock);
  1068			kcov_remote_area_put(area, size);
  1069			spin_unlock(&kcov_remote_lock);
  1070		}
  1071	
  1072		local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
  1073	
  1074		/* Get in kcov_remote_start(). */
  1075		kcov_put(kcov);
  1076	}
  1077	EXPORT_SYMBOL(kcov_remote_stop);
  1078	

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