Re: [PATCH 08/12] maple_tree: Separate ma_state node from status.

From: Liam R. Howlett
Date: Thu Nov 02 2023 - 13:39:41 EST

* kernel test robot <lkp@xxxxxxxxx> [231102 04:43]:
> Hi Liam,
>
> kernel test robot noticed the following build warnings:
>
> [auto build test WARNING on akpm-mm/mm-everything]
> [also build test WARNING on linus/master v6.6 next-20231102]
> [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/Liam-R-Howlett/maple_tree-Remove-unnecessary-default-labels-from-switch-statements/20231102-033618
> base: https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
> patch link: https://lore.kernel.org/r/20231101171629.3612299-9-Liam.Howlett%40oracle.com
> patch subject: [PATCH 08/12] maple_tree: Separate ma_state node from status.
> config: arc-randconfig-001-20231102 (https://download.01.org/0day-ci/archive/20231102/202311021622.6KoUHJP7-lkp@xxxxxxxxx/config)
> compiler: arceb-elf-gcc (GCC) 13.2.0
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20231102/202311021622.6KoUHJP7-lkp@xxxxxxxxx/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@xxxxxxxxx>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202311021622.6KoUHJP7-lkp@xxxxxxxxx/
>
> All warnings (new ones prefixed by >>):
>
> drivers/base/regmap/regcache-maple.c: In function 'regcache_maple_drop':
> drivers/base/regmap/regcache-maple.c:113:23: warning: 'lower_index' is used uninitialized [-Wuninitialized]
> 113 | unsigned long lower_index, lower_last;
> | ^~~~~~~~~~~
> drivers/base/regmap/regcache-maple.c:113:36: warning: 'lower_last' is used uninitialized [-Wuninitialized]
> 113 | unsigned long lower_index, lower_last;
> | ^~~~~~~~~~
> >> drivers/base/regmap/regcache-maple.c:114:23: warning: 'upper_index' is used uninitialized [-Wuninitialized]
> 114 | unsigned long upper_index, upper_last;
> | ^~~~~~~~~~~
> >> drivers/base/regmap/regcache-maple.c:114:36: warning: 'upper_last' is used uninitialized [-Wuninitialized]
> 114 | unsigned long upper_index, upper_last;
> | ^~~~~~~~~~
>

>From the above git blame, I can see that I didn't write any of this.
How did the bot blame my commits? It's interesting because it cannot be
randomly selecting the author of the data structure being used..

Also, I don't see how the bot is correct. Did you upgrade your bots GCC
and this is a false positive?


>
> vim +/upper_index +114 drivers/base/regmap/regcache-maple.c
>
> f033c26de5a5734 Mark Brown 2023-03-30 106
> f033c26de5a5734 Mark Brown 2023-03-30 107 static int regcache_maple_drop(struct regmap *map, unsigned int min,
> f033c26de5a5734 Mark Brown 2023-03-30 108 unsigned int max)
> f033c26de5a5734 Mark Brown 2023-03-30 109 {
> f033c26de5a5734 Mark Brown 2023-03-30 110 struct maple_tree *mt = map->cache;
> f033c26de5a5734 Mark Brown 2023-03-30 111 MA_STATE(mas, mt, min, max);
> f033c26de5a5734 Mark Brown 2023-03-30 112 unsigned long *entry, *lower, *upper;
> f033c26de5a5734 Mark Brown 2023-03-30 113 unsigned long lower_index, lower_last;
> f033c26de5a5734 Mark Brown 2023-03-30 @114 unsigned long upper_index, upper_last;
> f033c26de5a5734 Mark Brown 2023-03-30 115 int ret;
> f033c26de5a5734 Mark Brown 2023-03-30 116
> f033c26de5a5734 Mark Brown 2023-03-30 117 lower = NULL;

lower is null..

> f033c26de5a5734 Mark Brown 2023-03-30 118 upper = NULL;
> f033c26de5a5734 Mark Brown 2023-03-30 119
> f033c26de5a5734 Mark Brown 2023-03-30 120 mas_lock(&mas);
> f033c26de5a5734 Mark Brown 2023-03-30 121
> f033c26de5a5734 Mark Brown 2023-03-30 122 mas_for_each(&mas, entry, max) {
> f033c26de5a5734 Mark Brown 2023-03-30 123 /*
> f033c26de5a5734 Mark Brown 2023-03-30 124 * This is safe because the regmap lock means the
> f033c26de5a5734 Mark Brown 2023-03-30 125 * Maple lock is redundant, but we need to take it due
> f033c26de5a5734 Mark Brown 2023-03-30 126 * to lockdep asserts in the maple tree code.
> f033c26de5a5734 Mark Brown 2023-03-30 127 */
> f033c26de5a5734 Mark Brown 2023-03-30 128 mas_unlock(&mas);
> f033c26de5a5734 Mark Brown 2023-03-30 129
> f033c26de5a5734 Mark Brown 2023-03-30 130 /* Do we need to save any of this entry? */
> f033c26de5a5734 Mark Brown 2023-03-30 131 if (mas.index < min) {
> f033c26de5a5734 Mark Brown 2023-03-30 132 lower_index = mas.index;
> f033c26de5a5734 Mark Brown 2023-03-30 133 lower_last = min -1;
> f033c26de5a5734 Mark Brown 2023-03-30 134
> f033c26de5a5734 Mark Brown 2023-03-30 135 lower = kmemdup(entry, ((min - mas.index) *
> f033c26de5a5734 Mark Brown 2023-03-30 136 sizeof(unsigned long)),
> b0393e1fe40e962 Guenter Roeck 2023-07-20 137 map->alloc_flags);

Lower is only ever set here.. but lower_index/lower_last are also set
here..

> f033c26de5a5734 Mark Brown 2023-03-30 138 if (!lower) {
> f033c26de5a5734 Mark Brown 2023-03-30 139 ret = -ENOMEM;
> 451941ac1ee2be1 Mark Brown 2023-04-03 140 goto out_unlocked;
> f033c26de5a5734 Mark Brown 2023-03-30 141 }
> f033c26de5a5734 Mark Brown 2023-03-30 142 }
> f033c26de5a5734 Mark Brown 2023-03-30 143
> f033c26de5a5734 Mark Brown 2023-03-30 144 if (mas.last > max) {
> f033c26de5a5734 Mark Brown 2023-03-30 145 upper_index = max + 1;
> f033c26de5a5734 Mark Brown 2023-03-30 146 upper_last = mas.last;
> f033c26de5a5734 Mark Brown 2023-03-30 147
> f033c26de5a5734 Mark Brown 2023-03-30 148 upper = kmemdup(&entry[max + 1],
> f033c26de5a5734 Mark Brown 2023-03-30 149 ((mas.last - max) *
> f033c26de5a5734 Mark Brown 2023-03-30 150 sizeof(unsigned long)),
> b0393e1fe40e962 Guenter Roeck 2023-07-20 151 map->alloc_flags);
> f033c26de5a5734 Mark Brown 2023-03-30 152 if (!upper) {
> f033c26de5a5734 Mark Brown 2023-03-30 153 ret = -ENOMEM;
> 451941ac1ee2be1 Mark Brown 2023-04-03 154 goto out_unlocked;
> f033c26de5a5734 Mark Brown 2023-03-30 155 }
> f033c26de5a5734 Mark Brown 2023-03-30 156 }
> f033c26de5a5734 Mark Brown 2023-03-30 157
> f033c26de5a5734 Mark Brown 2023-03-30 158 kfree(entry);
> f033c26de5a5734 Mark Brown 2023-03-30 159 mas_lock(&mas);
> f033c26de5a5734 Mark Brown 2023-03-30 160 mas_erase(&mas);
> f033c26de5a5734 Mark Brown 2023-03-30 161
> f033c26de5a5734 Mark Brown 2023-03-30 162 /* Insert new nodes with the saved data */
> f033c26de5a5734 Mark Brown 2023-03-30 163 if (lower) {

Only used if lower isn't NULL, so we know lower_index and lower_last are
set.

> f033c26de5a5734 Mark Brown 2023-03-30 164 mas_set_range(&mas, lower_index, lower_last);
> b0393e1fe40e962 Guenter Roeck 2023-07-20 165 ret = mas_store_gfp(&mas, lower, map->alloc_flags);
> f033c26de5a5734 Mark Brown 2023-03-30 166 if (ret != 0)
> f033c26de5a5734 Mark Brown 2023-03-30 167 goto out;
> f033c26de5a5734 Mark Brown 2023-03-30 168 lower = NULL;

lower is reset for the next loop.

> f033c26de5a5734 Mark Brown 2023-03-30 169 }
> f033c26de5a5734 Mark Brown 2023-03-30 170
> f033c26de5a5734 Mark Brown 2023-03-30 171 if (upper) {
> f033c26de5a5734 Mark Brown 2023-03-30 172 mas_set_range(&mas, upper_index, upper_last);
> b0393e1fe40e962 Guenter Roeck 2023-07-20 173 ret = mas_store_gfp(&mas, upper, map->alloc_flags);
> f033c26de5a5734 Mark Brown 2023-03-30 174 if (ret != 0)
> f033c26de5a5734 Mark Brown 2023-03-30 175 goto out;
> f033c26de5a5734 Mark Brown 2023-03-30 176 upper = NULL;
> f033c26de5a5734 Mark Brown 2023-03-30 177 }
> f033c26de5a5734 Mark Brown 2023-03-30 178 }
> f033c26de5a5734 Mark Brown 2023-03-30 179
> f033c26de5a5734 Mark Brown 2023-03-30 180 out:
> f033c26de5a5734 Mark Brown 2023-03-30 181 mas_unlock(&mas);
> 451941ac1ee2be1 Mark Brown 2023-04-03 182 out_unlocked:
> f033c26de5a5734 Mark Brown 2023-03-30 183 kfree(lower);
> f033c26de5a5734 Mark Brown 2023-03-30 184 kfree(upper);
> f033c26de5a5734 Mark Brown 2023-03-30 185
> f033c26de5a5734 Mark Brown 2023-03-30 186 return ret;
> f033c26de5a5734 Mark Brown 2023-03-30 187 }
> f033c26de5a5734 Mark Brown 2023-03-30 188
>
> --
> 0-DAY CI Kernel Test Service
> https://github.com/intel/lkp-tests/wiki