[PATCH] Btrfs: fix compile error about uninitialized variable

[PATCH] Btrfs: fix compile error about uninitialized variable

[ye.xingchen]

From: Minghao Chi <chi.minghao@zte.com.cn>

fs/btrfs/tree-log.c:6166:6: note: 'last_range_start' was declared here
fs/btrfs/volumes.c:2598:27: note: 'seed_devices' was declared here
fs/btrfs/send.c:1909:13: error: 'right_gen' may be used uninitialized in this function [-Werror=maybe-uninitialized]

Signed-off-by: Minghao Chi <chi.minghao@zte.com.cn>
Signed-off-by: ye xingchen <ye.xingchen@zte.com.cn>
---
 fs/btrfs/send.c     | 2 +-
 fs/btrfs/tree-log.c | 2 +-
 fs/btrfs/volumes.c  | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index c3146ce84156..3c9f2d30065d 100644
--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -1875,7 +1875,7 @@ static int get_cur_inode_state(struct send_ctx *sctx, u64 ino, u64 gen,
 	int left_ret;
 	int right_ret;
 	u64 left_gen;
-	u64 right_gen;
+	u64 right_gen = 0;
 	struct btrfs_inode_info info;

 	ret = get_inode_info(sctx->send_root, ino, &info);
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index 200cea6e49e5..b91fa398b814 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -6163,7 +6163,7 @@ 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;

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 83cb2db43779..1298569cf8b5 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -2595,7 +2595,7 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path
 	struct block_device *bdev;
 	struct super_block *sb = fs_info->sb;
 	struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
-	struct btrfs_fs_devices *seed_devices;
+	struct btrfs_fs_devices *seed_devices = NULL;
 	u64 orig_super_total_bytes;
 	u64 orig_super_num_devices;
 	int ret = 0;
-- 
2.25.1

Re: [PATCH] Btrfs: fix compile error about uninitialized variable

[Qu Wenruo]

On 2023/2/1 10:22, ye.xingchen@zte.com.cn wrote:
> From: Minghao Chi <chi.minghao@zte.com.cn>
> 
> fs/btrfs/tree-log.c:6166:6: note: 'last_range_start' was declared here
> fs/btrfs/volumes.c:2598:27: note: 'seed_devices' was declared here
> fs/btrfs/send.c:1909:13: error: 'right_gen' may be used uninitialized in this function [-Werror=maybe-uninitialized]

Have you really dig into the code?

When @right_gen is not initialized, we have @right_ret assigned to -ENOENT.

Thus all later code checking @right_gen would not be executed, and this 
is a false alert.

You should explain this is a false alert first.

Secondly it's easy to just stick a "= 0" to whatever compiler complains 
in this case, but since it's a false alert, you really need to explain 
your compiler version to see if it's really better to fix in the code 
other than your compiler.

> 
> Signed-off-by: Minghao Chi <chi.minghao@zte.com.cn>
> Signed-off-by: ye xingchen <ye.xingchen@zte.com.cn>
> ---
>   fs/btrfs/send.c     | 2 +-
>   fs/btrfs/tree-log.c | 2 +-
>   fs/btrfs/volumes.c  | 2 +-
>   3 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
> index c3146ce84156..3c9f2d30065d 100644
> --- a/fs/btrfs/send.c
> +++ b/fs/btrfs/send.c
> @@ -1875,7 +1875,7 @@ static int get_cur_inode_state(struct send_ctx *sctx, u64 ino, u64 gen,
>   	int left_ret;
>   	int right_ret;
>   	u64 left_gen;
> -	u64 right_gen;
> +	u64 right_gen = 0;
>   	struct btrfs_inode_info info;
> 
>   	ret = get_inode_info(sctx->send_root, ino, &info);
> diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
> index 200cea6e49e5..b91fa398b814 100644
> --- a/fs/btrfs/tree-log.c
> +++ b/fs/btrfs/tree-log.c
> @@ -6163,7 +6163,7 @@ 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;
> 
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 83cb2db43779..1298569cf8b5 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -2595,7 +2595,7 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path
>   	struct block_device *bdev;
>   	struct super_block *sb = fs_info->sb;
>   	struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
> -	struct btrfs_fs_devices *seed_devices;
> +	struct btrfs_fs_devices *seed_devices = NULL;
>   	u64 orig_super_total_bytes;
>   	u64 orig_super_num_devices;
>   	int ret = 0;

Re: [PATCH] Btrfs: fix compile error about uninitialized variable

[David Sterba]

On Wed, Feb 01, 2023 at 10:22:19AM +0800, ye.xingchen@zte.com.cn wrote:
> From: Minghao Chi <chi.minghao@zte.com.cn>
> 
> fs/btrfs/tree-log.c:6166:6: note: 'last_range_start' was declared here
> fs/btrfs/volumes.c:2598:27: note: 'seed_devices' was declared here
> fs/btrfs/send.c:1909:13: error: 'right_gen' may be used uninitialized in this function [-Werror=maybe-uninitialized]

We have the warning -Wmaybe-uninitialized enabled locally for fs/btrfs/
and no pending compiler warnings but in case you find something please
tell us which compiler and version it is. Sometimes it makes sense to
fix warnings for older yet still widely used versions.