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

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Date:   Mon, 21 Feb 2022 08:15:52 +0800
From:   Qu Wenruo <quwenruo.btrfs@....com>
To:     Souptick Joarder <jrdr.linux@...il.com>, clm@...com,
        josef@...icpanda.com, dsterba@...e.com, nathan@...nel.org,
        ndesaulniers@...gle.com
Cc:     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 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.

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 &&