Re: [PATCH] btrfs: fix uninitialized warning in btrfs_log_inode

[Anand Jain]

On 17/5/23 15:46, Qu Wenruo wrote:
> On 2023/5/16 09:34, zhangshida wrote:
> > From: Shida Zhang <zhangshida@xxxxxxxxxx>
> >
> > From: Shida Zhang <zhangshida@xxxxxxxxxx>
> >
> > 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.

I also noticed that last_range_start is not actually uninitialized.
However, it is acceptable to initialize a variable to silence the
compiler if necessary, right? We have done something similar in the
past.

Thanks, Anand

> @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@xxxxxxxxxx>
> > Signed-off-by: Shida Zhang <zhangshida@xxxxxxxxxx>
> > ---
> >   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;