Re: [PATCH 05/22] btrfs: add the beginning of async discard, discard workqueue

[Nick Desaulniers <ndesaulniers@google.com>]

Hi Dennis,
Below is a 0day bot report from a build w/ Clang. Warning looks legit,
can you please take a look?

On Thu, Nov 21, 2019 at 11:27 AM kbuild test robot <lkp@intel.com> wrote:
>
> CC: kbuild-all@lists.01.org
> In-Reply-To: <63d3257efe1158a6fbbd7abe865cd9250b494438.1574282259.git.dennis@kernel.org>
> References: <63d3257efe1158a6fbbd7abe865cd9250b494438.1574282259.git.dennis@kernel.org>
> TO: Dennis Zhou <dennis@kernel.org>
> CC: David Sterba <dsterba@suse.com>, Chris Mason <clm@fb.com>, Josef Bacik <josef@toxicpanda.com>, Omar Sandoval <osandov@osandov.com>
> CC: kernel-team@fb.com, linux-btrfs@vger.kernel.org, Dennis Zhou <dennis@kernel.org>
>
> Hi Dennis,
>
> I love your patch! Perhaps something to improve:
>
> [auto build test WARNING on kdave/for-next]
> [also build test WARNING on next-20191121]
> [cannot apply to v5.4-rc8]
> [if your patch is applied to the wrong git tree, please drop us a note to help
> improve the system. BTW, we also suggest to use '--base' option to specify the
> base tree in git format-patch, please see https://stackoverflow.com/a/37406982]
>
> url:    https://github.com/0day-ci/linux/commits/Dennis-Zhou/btrfs-async-discard-support/20191121-230429
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux.git for-next
> config: arm64-defconfig (attached as .config)
> compiler: clang version 10.0.0 (git://gitmirror/llvm_project cf823ce4ad9d04c69b7c29d236f7b14c875111c2)
> reproduce:
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # save the attached .config to linux build tree
>         make.cross ARCH=arm64
>
> If you fix the issue, kindly add following tag
> Reported-by: kbuild test robot <lkp@intel.com>
>
> All warnings (new ones prefixed by >>):
>
> >> fs/btrfs/free-space-cache.c:3238:6: warning: variable 'trim_state' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
>            if (!ret) {
>                ^~~~
>    fs/btrfs/free-space-cache.c:3251:53: note: uninitialized use occurs here
>            __btrfs_add_free_space(fs_info, ctl, start, bytes, trim_state);
>                                                               ^~~~~~~~~~
>    fs/btrfs/free-space-cache.c:3238:2: note: remove the 'if' if its condition is always true
>            if (!ret) {
>            ^~~~~~~~~~
>    fs/btrfs/free-space-cache.c:3224:2: note: variable 'trim_state' is declared here
>            enum btrfs_trim_state trim_state;
>            ^
>    1 warning generated.
>
> vim +3238 fs/btrfs/free-space-cache.c
>
>   3210
>   3211  static int do_trimming(struct btrfs_block_group *block_group,
>   3212                         u64 *total_trimmed, u64 start, u64 bytes,
>   3213                         u64 reserved_start, u64 reserved_bytes,
>   3214                         enum btrfs_trim_state reserved_trim_state,
>   3215                         struct btrfs_trim_range *trim_entry)
>   3216  {
>   3217          struct btrfs_space_info *space_info = block_group->space_info;
>   3218          struct btrfs_fs_info *fs_info = block_group->fs_info;
>   3219          struct btrfs_free_space_ctl *ctl = block_group->free_space_ctl;
>   3220          int ret;
>   3221          int update = 0;
>   3222          u64 end = start + bytes;
>   3223          u64 reserved_end = reserved_start + reserved_bytes;
>   3224          enum btrfs_trim_state trim_state;
>   3225          u64 trimmed = 0;
>   3226
>   3227          spin_lock(&space_info->lock);
>   3228          spin_lock(&block_group->lock);
>   3229          if (!block_group->ro) {
>   3230                  block_group->reserved += reserved_bytes;
>   3231                  space_info->bytes_reserved += reserved_bytes;
>   3232                  update = 1;
>   3233          }
>   3234          spin_unlock(&block_group->lock);
>   3235          spin_unlock(&space_info->lock);
>   3236
>   3237          ret = btrfs_discard_extent(fs_info, start, bytes, &trimmed);
> > 3238          if (!ret) {
>   3239                  *total_trimmed += trimmed;
>   3240                  trim_state = BTRFS_TRIM_STATE_TRIMMED;
>   3241          }
>   3242
>   3243          mutex_lock(&ctl->cache_writeout_mutex);
>   3244          if (reserved_start < start)
>   3245                  __btrfs_add_free_space(fs_info, ctl, reserved_start,
>   3246                                         start - reserved_start,
>   3247                                         reserved_trim_state);
>   3248          if (start + bytes < reserved_start + reserved_bytes)
>   3249                  __btrfs_add_free_space(fs_info, ctl, end, reserved_end - end,
>   3250                                         reserved_trim_state);
>   3251          __btrfs_add_free_space(fs_info, ctl, start, bytes, trim_state);

^ oops

>   3252          list_del(&trim_entry->list);
>   3253          mutex_unlock(&ctl->cache_writeout_mutex);
>   3254
>   3255          if (update) {
>   3256                  spin_lock(&space_info->lock);
>   3257                  spin_lock(&block_group->lock);
>   3258                  if (block_group->ro)
>   3259                          space_info->bytes_readonly += reserved_bytes;
>   3260                  block_group->reserved -= reserved_bytes;
>   3261                  space_info->bytes_reserved -= reserved_bytes;
>   3262                  spin_unlock(&block_group->lock);
>   3263                  spin_unlock(&space_info->lock);
>   3264          }
>   3265
>   3266          return ret;
>   3267  }
>   3268
>
> ---
> 0-DAY kernel test infrastructure                 Open Source Technology Center
> https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org Intel Corporation



-- 
Thanks,
~Nick Desaulniers