linux-kernel - Re: [PATCH] btrfs: fix uninitialized warning in btrfs_log

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Date:   Wed, 17 May 2023 15:46:40 +0800
From:   Qu Wenruo <quwenruo.btrfs@....com>
To:     zhangshida <starzhangzsd@...il.com>, clm@...com,
        josef@...icpanda.com, dsterba@...e.com
Cc:     linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org,
        zhangshida@...inos.cn, k2ci <kernel-bot@...inos.cn>
Subject: Re: [PATCH] btrfs: fix uninitialized warning in btrfs_log_inode



On 2023/5/16 09:34, zhangshida wrote:
> From: Shida Zhang <zhangshida@...inos.cn>
>
> From: Shida Zhang <zhangshida@...inos.cn>
>
> This fixes the following warning reported by gcc 10 under x86_64:

Full gcc version please.
Especially you need to check if your gcc10 is the latest release.

If newer gcc (12.2.1) tested without such error, it may very possible to
be a false alert.

And in fact it is.

@first_dir_index would only be assigned to @last_range_start if
last_range_end != 0.

Thus the loop must have to be executed once, and @last_range_start won't
be zero.

Please do check your environment (especially your gcc version and
backports), before sending such trivial patches.
Under most cases, it helps nobody.

Thanks,
Qu

>
> ../fs/btrfs/tree-log.c: In function ‘btrfs_log_inode’:
> ../fs/btrfs/tree-log.c:6211:9: error: ‘last_range_start’ may be used uninitialized in this function [-Werror=maybe-uninitialized]
>   6211 |   ret = insert_dir_log_key(trans, log, path, key.objectid,
>        |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   6212 |       first_dir_index, last_dir_index);
>        |       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> ../fs/btrfs/tree-log.c:6161:6: note: ‘last_range_start’ was declared here
>   6161 |  u64 last_range_start;
>        |      ^~~~~~~~~~~~~~~~
>
> Reported-by: k2ci <kernel-bot@...inos.cn>
> Signed-off-by: Shida Zhang <zhangshida@...inos.cn>
> ---
>   fs/btrfs/tree-log.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
> index 9b212e8c70cc..d2755d5e338b 100644
> --- a/fs/btrfs/tree-log.c
> +++ b/fs/btrfs/tree-log.c
> @@ -6158,7 +6158,7 @@ static int log_delayed_deletions_incremental(struct btrfs_trans_handle *trans,
>   {
>   	struct btrfs_root *log = inode->root->log_root;
>   	const struct btrfs_delayed_item *curr;
> -	u64 last_range_start;
> +	u64 last_range_start = 0;
>   	u64 last_range_end = 0;
>   	struct btrfs_key key;
>