Re: [PATCH] btrfs: work around false-positive -Wsometimes-uninitialized warning

From: Nikolay Borisov <nborisov@suse.com>
To: Arnd Bergmann <arnd@arndb.de>, Chris Mason <clm@fb.com>,
	Josef Bacik <josef@toxicpanda.com>,
	David Sterba <dsterba@suse.com>
Cc: clang-built-linux@googlegroups.com,
	Nick Desaulniers <ndesaulniers@google.com>,
	Nathan Chancellor <natechancellor@gmail.com>,
	Lu Fengqi <lufq.fnst@cn.fujitsu.com>,
	Anand Jain <anand.jain@oracle.com>,
	linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] btrfs: work around false-positive -Wsometimes-uninitialized warning
Date: Fri, 22 Mar 2019 16:11:52 +0200	[thread overview]
Message-ID: <57833895-fce3-75bc-a28e-6bdc6d14ea8c@suse.com> (raw)
In-Reply-To: <20190322140753.286171-1-arnd@arndb.de>

On 22.03.19 г. 16:07 ч., Arnd Bergmann wrote:
> clang fails to see that the last 'else if() in btrfs_uuid_tree_add()
> is always true, so 'eb' is always initialized correctly:
> 
> fs/btrfs/uuid-tree.c:129:13: error: variable 'eb' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]
>         } else if (ret < 0) {
>                    ^~~~~~~
> fs/btrfs/uuid-tree.c:139:22: note: uninitialized use occurs here
>         write_extent_buffer(eb, &subid_le, offset, sizeof(subid_le));
>                             ^~
> fs/btrfs/uuid-tree.c:129:9: note: remove the 'if' if its condition is always true
>         } else if (ret < 0) {
>                ^~~~~~~~~~~~~
> fs/btrfs/uuid-tree.c:90:26: note: initialize the variable 'eb' to silence this warning
>         struct extent_buffer *eb;
>                                 ^
>                                  = NULL
> 
> Change it into a plain 'else' to shut up that warning.
> 
> Link: https://bugs.llvm.org/show_bug.cgi?id=41197
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Such a patch has already been merged to misc-next:

f22898caa6a5 ("btrfs: Turn an 'else if' into an 'else' in
btrfs_uuid_tree_add")

> ---
>  fs/btrfs/uuid-tree.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/uuid-tree.c b/fs/btrfs/uuid-tree.c
> index 3b2ae342e649..c1cc9a5c0024 100644
> --- a/fs/btrfs/uuid-tree.c
> +++ b/fs/btrfs/uuid-tree.c
> @@ -126,7 +126,7 @@ int btrfs_uuid_tree_add(struct btrfs_trans_handle *trans, u8 *uuid, u8 type,
>  		slot = path->slots[0];
>  		offset = btrfs_item_ptr_offset(eb, slot);
>  		offset += btrfs_item_size_nr(eb, slot) - sizeof(subid_le);
> -	} else if (ret < 0) {
> +	} else {
>  		btrfs_warn(fs_info,
>  			   "insert uuid item failed %d (0x%016llx, 0x%016llx) type %u!",
>  			   ret, (unsigned long long)key.objectid,
> 