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Date:   Tue, 30 May 2023 16:32:34 -0700
From:   Jaegeuk Kim <jaegeuk@kernel.org>
To:     Wu Bo <bo.wu@vivo.com>
Cc:     Chao Yu <chao@kernel.org>, linux-f2fs-devel@lists.sourceforge.net,
        linux-kernel@vger.kernel.org, wubo.oduw@gmail.com
Subject: Re: [PATCH v2 1/1] f2fs: fix args passed to trace_f2fs_lookup_end
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References: <20230530012118.74228-1-bo.wu@vivo.com>
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On 05/30, Wu Bo wrote:
> The NULL return of 'd_splice_alias' dosen't mean error. Thus the
> successful case will also return NULL, which makes the tracepoint always
> print 'err=-ENOENT'.
> 
> Signed-off-by: Wu Bo <bo.wu@vivo.com>
> ---
>  fs/f2fs/namei.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/f2fs/namei.c b/fs/f2fs/namei.c
> index 77a71276ecb1..0c5e4c424eab 100644
> --- a/fs/f2fs/namei.c
> +++ b/fs/f2fs/namei.c
> @@ -576,8 +576,9 @@ static struct dentry *f2fs_lookup(struct inode *dir, struct dentry *dentry,
>  	}
>  #endif
>  	new = d_splice_alias(inode, dentry);
> -	err = PTR_ERR_OR_ZERO(new);
> -	trace_f2fs_lookup_end(dir, dentry, ino, !new ? -ENOENT : err);
> +	if (IS_ERR(new))
> +		err = PTR_ERR(new);
> +	trace_f2fs_lookup_end(dir, new ? new : dentry, ino, err);

Again, new can be an error pointer, and the previous err was supposed to be
zero or -ENOENT.

case 1) dentry exists: err (0) with new (NULL) --> dentry, err=0
case 2) dentry exists: err (0) with new (VALID) --> new, err=0
case 3) dentry exists: err (0) with new (ERR) --> dentry, err=ERR
case 4) no dentry exists: err (-ENOENT) with new (NULL) --> dentry, err=-ENOENT
case 4) no dentry exists: err (-ENOENT) with new (VALID) --> new, err=-ENOENT
case 5) no dentry exists: err (-ENOENT) with new (ERR) --> dentry, err=ERR

	trace_f2fs_lookup_end(dir, !IS_ERR_OR_NULL(new) ? new : dentry,
				ino, IS_ERR(new) ? PTR_ERR(new) : err);


>  	return new;
>  out_iput:
>  	iput(inode);
> -- 
> 2.35.3