linux-kernel - Re: [PATCH] btrfs: Turn an 'else if' into an 'else' in btrfs_uuid_tree

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Message-ID: <CAKwvOd=SY7wOD0UTXcqcY7ugprOMgbbb8y0Z-rTGQpBqRJ8YaQ@mail.gmail.com>
Date:   Thu, 7 Mar 2019 09:58:14 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     dsterba@...e.cz, Nathan Chancellor <natechancellor@...il.com>,
        Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>, linux-btrfs@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux@...glegroups.com,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH] btrfs: Turn an 'else if' into an 'else' in btrfs_uuid_tree_add

On Thu, Mar 7, 2019 at 9:54 AM David Sterba <dsterba@...e.cz> wrote:
>
> On Thu, Mar 07, 2019 at 09:35:15AM -0700, Nathan Chancellor wrote:
> > When building with -Wsometimes-uninitialized, Clang warns:
> >
> > fs/btrfs/uuid-tree.c:129:13: warning: variable 'eb' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
> > fs/btrfs/uuid-tree.c:129:13: warning: variable 'offset' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
> >
> > Clang can't tell that all cases are covered with this final else if.
>
> The chain of conditions is
>
> if (ret >= 0)
> else if (ret == -EEXIST)
> else if (ret < 0)

In the few cases we looked at, it seemed that the compiler's heuristic
for coverage doesn't try very hard.  I assume once you start having
more complicated expressions is gets quite difficult to prove.

Thanks for the patch Nathan!
-- 
Thanks,
~Nick Desaulniers