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

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Message-ID: <20190322142540.GC28481@twin.jikos.cz>
Date:   Fri, 22 Mar 2019 15:25:40 +0100
From:   David Sterba <dsterba@...e.cz>
To:     Nikolay Borisov <nborisov@...e.com>
Cc:     Arnd Bergmann <arnd@...db.de>, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>,
        clang-built-linux@...glegroups.com,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Lu Fengqi <lufq.fnst@...fujitsu.com>,
        Anand Jain <anand.jain@...cle.com>,
        linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] btrfs: work around false-positive
 -Wsometimes-uninitialized warning

On Fri, Mar 22, 2019 at 04:11:52PM +0200, Nikolay Borisov wrote:
> 
> 
> 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@...db.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")

I haven't updated for-next for a few days so the patch was not so
visible outside, will push an update today.