linux-kernel - Re: [PATCH] btrfs: fix build warning

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Message-ID: <CAMuHMdVfCP97jKauZ5j29zAnWPi0ro_hRkq=A0AS=N6jgPHdwA@mail.gmail.com>
Date:	Tue, 22 Mar 2016 10:39:59 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Sudip Mukherjee <sudipm.mukherjee@...il.com>
Cc:	Chris Mason <clm@...com>, Josef Bacik <jbacik@...com>,
	David Sterba <dsterba@...e.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-btrfs <linux-btrfs@...r.kernel.org>
Subject: Re: [PATCH] btrfs: fix build warning

On Tue, Feb 16, 2016 at 9:02 AM, Sudip Mukherjee
<sudipm.mukherjee@...il.com> wrote:
> We were getting build warning about:
> fs/btrfs/extent-tree.c:7021:34: warning: ‘used_bg’ may be used
>         uninitialized in this function
>
> It is not a valid warning as used_bg is never used uninitilized since
> locked is initially false so we can never be in the section where
> 'used_bg' is used. But gcc is not able to understand that and we can
> initialize it while declaring to silence the warning.
>
> Signed-off-by: Sudip Mukherjee <sudip@...torindia.org>

FWIW, I've posted an alternative patch that killed the silly locked variable
a while ago.
"[PATCH] Btrfs: Refactor btrfs_lock_cluster() to kill compiler warning"
https://lkml.org/lkml/2014/6/22/96

> ---
>  fs/btrfs/extent-tree.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index e2287c7..f24e4c3 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -7018,7 +7018,7 @@ btrfs_lock_cluster(struct btrfs_block_group_cache *block_group,
>                    struct btrfs_free_cluster *cluster,
>                    int delalloc)
>  {
> -       struct btrfs_block_group_cache *used_bg;
> +       struct btrfs_block_group_cache *used_bg = NULL;
>         bool locked = false;
>  again:
>         spin_lock(&cluster->refill_lock);
> --
> 1.9.1

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds