Re: [PATCH v1] btrfs: discard: fix warning for discard_state

[Qu Wenruo <wqu@suse.com>]

在 2026/9/14 18:52, Jiahao Li 写道:
> From: Jiahao Li <lijiahao1@kylinos.cn>
> 
> Building with -Werror=mabe-uninitialized fails:
> fs/btrfs/discard.c:553:9: error: 'discard_state' may be used
> uninitialized [-Werror=maybe-uninitialized]
> 
> The compiler cannot prove that discard_state is assigned on every path
> before it is read.

Compiler and its version, a lot of times such false alerts are just 
compiler version dependent.

In my case, gcc 16.2.1 failed to reproduced this false alert.

  Initialize it to BTRFS_DISCARD_EXTENTS, which is the
> state the variable holds when the loop is first entered, this does not
> change runtime behavior, so the warning is gone and the value is always
> well defined.

It's a false alert.

Firstly if peek_discard_list() didn't find a bg, btrfs_discard_workfn() 
returned immediately.

Secondly if a bg is found in peek_discard_list(), *discard_state is 
fetched from bg's discard_state.

So all paths should be fine.

> 
> Signed-off-by: Jiahao Li <lijiahao1@kylinos.cn>
> ---
>   fs/btrfs/discard.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/discard.c b/fs/btrfs/discard.c
> index 1c304bf473e5..413a804ff46b 100644
> --- a/fs/btrfs/discard.c
> +++ b/fs/btrfs/discard.c
> @@ -519,7 +519,7 @@ static void btrfs_discard_workfn(struct work_struct *work)
>   {
>   	struct btrfs_discard_ctl *discard_ctl;
>   	struct btrfs_block_group *block_group;
> -	enum btrfs_discard_state discard_state;
> +	enum btrfs_discard_state discard_state = BTRFS_DISCARD_EXTENTS;
>   	int discard_index = 0;
>   	u64 trimmed = 0;
>   	u64 minlen = 0;