linux-kernel - Re: [PATCH] btrfs: Initialize ret to 0 in scrub_simple

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Message-ID: <CAFqt6zZsv+bMwbdqrcOMCZE08O_q7DGa0ejVAbokLybsSch5fw@mail.gmail.com>
Date:   Tue, 22 Feb 2022 13:20:45 +0530
From:   Souptick Joarder <jrdr.linux@...il.com>
To:     Qu Wenruo <quwenruo.btrfs@....com>
Cc:     Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>,
        dsterba@...e.com, nathan@...nel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] btrfs: Initialize ret to 0 in scrub_simple_mirror()

On Mon, Feb 21, 2022 at 5:46 AM Qu Wenruo <quwenruo.btrfs@....com> wrote:
>
>
>
> On 2022/2/20 22:46, Souptick Joarder wrote:
> > From: "Souptick Joarder (HPE)" <jrdr.linux@...il.com>
> >
> > Kernel test robot reported below warning ->
> > fs/btrfs/scrub.c:3439:2: warning: Undefined or garbage value
> > returned to caller [clang-analyzer-core.uninitialized.UndefReturn]
> >
> > Initialize ret to 0.
> >
> > Reported-by: kernel test robot <lkp@...el.com>
> > Signed-off-by: Souptick Joarder (HPE) <jrdr.linux@...il.com>
>
> Although the patch is not yet merged, but I have to say, it's a false alert.

Yes, I agree it is a false positive but this patch will at least keep
kernel test robot happy :)
>
> Firstly, the while loop will always get at least one run.
>
> Secondly, in that loop, we either set ret to some error value and break,
> or after at least one find_first_extent_item() and scrub_extent() call,
> we increase cur_logical and reached the limit of the while loop and exit.
>
> So there is no possible routine to leave @ret uninitialized and returned
> to caller.
>
> Thanks,
> Qu
>
> > ---
> >   fs/btrfs/scrub.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
> > index 4baa8e43d585..5ca7e5ffbc96 100644
> > --- a/fs/btrfs/scrub.c
> > +++ b/fs/btrfs/scrub.c
> > @@ -3325,7 +3325,7 @@ static int scrub_simple_mirror(struct scrub_ctx *sctx,
> >       const u32 max_length = SZ_64K;
> >       struct btrfs_path path = {};
> >       u64 cur_logical = logical_start;
> > -     int ret;
> > +     int ret = 0;
> >
> >       /* The range must be inside the bg */
> >       ASSERT(logical_start >= bg->start &&