linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: get parent inode when recovering pino

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Date:   Tue, 5 May 2020 09:58:47 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net, kernel-team@...roid.com
Subject: Re: [f2fs-dev] [PATCH] f2fs: get parent inode when recovering pino

On Tue, May 05, 2020 at 08:31:39AM -0700, Jaegeuk Kim wrote:
> We had to grab the inode before retrieving i_ino.
> 
> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> ---
>  fs/f2fs/file.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index a0a4413d6083b..9d4c3e3503567 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -168,6 +168,7 @@ static const struct vm_operations_struct f2fs_file_vm_ops = {
>  static int get_parent_ino(struct inode *inode, nid_t *pino)
>  {
>  	struct dentry *dentry;
> +	struct inode *parent;
>  
>  	inode = igrab(inode);
>  	dentry = d_find_any_alias(inode);
> @@ -175,8 +176,13 @@ static int get_parent_ino(struct inode *inode, nid_t *pino)
>  	if (!dentry)
>  		return 0;
>  
> -	*pino = parent_ino(dentry);
> +	parent = igrab(d_inode(dentry->d_parent));
>  	dput(dentry);
> +	if (!parent)
> +		return 0;
> +
> +	*pino = parent->i_ino;
> +	iput(parent);
>  	return 1;

This doesn't appear to be necessary.  parent_ino() is:

	spin_lock(&dentry->d_lock);
	res = dentry->d_parent->d_inode->i_ino;
	spin_unlock(&dentry->d_lock);

Since dentry is locked and referenced, ->d_parent is stable and positive.

In the encrypt+casefold patch I was reviewing, it's indeed necessary, but only
because there was a check of inode->i_flags added outside the locked region.
The following would be simpler:

        spin_lock(&dentry->d_lock);
        dir = dentry->d_parent->d_inode;
        *pino = dir->i_ino;
        needs_recovery = IS_ENCRYPTED(dir) && IS_CASEFOLDED(dir);
        spin_unlock(&dentry->d_lock);

BTW, d_find_any_alias() is unnecessary too.  This code should just be using
file_dentry(file) from f2fs_do_sync_file().

- Eric