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

[Eric Biggers <ebiggers@kernel.org>]

On Tue, May 05, 2020 at 09:58:47AM -0700, Eric Biggers wrote:
> 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@kernel.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().
> 

Also, what is this code trying to accomplish?  If it's trying to find the parent
directory of an inode with i_nlink == 1, this isn't the correct way to do it.
The fsync could be done via a deleted file, which would make the wrong p_ino be
set.  I think the correct approach would be to iterate through all the dentry's
aliases, and choose the parent directory that's !IS_DEADDIR().

- Eric