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Date:   Tue, 5 May 2020 11:19:41 -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 11:13:23AM -0700, Jaegeuk Kim wrote:
> On 05/05, 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@...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;
> 
> Hi Eric,
> 
> > 
> > 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.
> 
> I see, thanks. :)
> 
> > 
> > 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);
> 
> Ack.
> 
> > 
> > BTW, d_find_any_alias() is unnecessary too.  This code should just be using
> > file_dentry(file) from f2fs_do_sync_file().
> 
> How about this?
> 
> From 9aee969a413b1ed22b48573071bc93fbb4a2002d Mon Sep 17 00:00:00 2001
> From: Jaegeuk Kim <jaegeuk@...nel.org>
> Date: Tue, 5 May 2020 11:08:58 -0700
> Subject: [PATCH] f2fs: remove unnecessary dentry locks
> 
> As Eric commented, let's kill unnecessary dentry ops when recovering
> parent inode number.
> 
> Suggested-by: Eric Biggers <ebiggers@...nel.org>
> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> ---
>  fs/f2fs/file.c | 26 ++++++--------------------
>  1 file changed, 6 insertions(+), 20 deletions(-)
> 
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index a0a4413d6083b..711cebad36fc5 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -165,21 +165,6 @@ static const struct vm_operations_struct f2fs_file_vm_ops = {
>  	.page_mkwrite	= f2fs_vm_page_mkwrite,
>  };
>  
> -static int get_parent_ino(struct inode *inode, nid_t *pino)
> -{
> -	struct dentry *dentry;
> -
> -	inode = igrab(inode);
> -	dentry = d_find_any_alias(inode);
> -	iput(inode);
> -	if (!dentry)
> -		return 0;
> -
> -	*pino = parent_ino(dentry);
> -	dput(dentry);
> -	return 1;
> -}
> -
>  static inline enum cp_reason_type need_do_checkpoint(struct inode *inode)
>  {
>  	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
> @@ -223,14 +208,15 @@ static bool need_inode_page_update(struct f2fs_sb_info *sbi, nid_t ino)
>  	return ret;
>  }
>  
> -static void try_to_fix_pino(struct inode *inode)
> +static void try_to_fix_pino(struct dentry *dentry)
>  {
> +	struct inode *inode = d_inode(dentry);
>  	struct f2fs_inode_info *fi = F2FS_I(inode);
> -	nid_t pino;
>  
>  	down_write(&fi->i_sem);
> -	if (file_wrong_pino(inode) && inode->i_nlink == 1 &&
> -			get_parent_ino(inode, &pino)) {
> +	if (file_wrong_pino(inode) && inode->i_nlink == 1) {
> +		nid_t pino = parent_ino(dentry);
> +
>  		f2fs_i_pino_write(inode, pino);
>  		file_got_pino(inode);
>  	}
> @@ -310,7 +296,7 @@ static int f2fs_do_sync_file(struct file *file, loff_t start, loff_t end,
>  		 * We've secured consistency through sync_fs. Following pino
>  		 * will be used only for fsynced inodes after checkpoint.
>  		 */
> -		try_to_fix_pino(inode);
> +		try_to_fix_pino(file_dentry(file));
>  		clear_inode_flag(inode, FI_APPEND_WRITE);
>  		clear_inode_flag(inode, FI_UPDATE_WRITE);
>  		goto out;

Actually, I think this is wrong because the fsync can be done via a file
descriptor that was opened to a now-deleted link to the file.

We need to find the dentry whose parent directory is still exists, i.e. the
parent directory that is counting towards 'inode->i_nlink == 1'.

I think d_find_alias() is what we're looking for.

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 6ab8f621a3c5..855f27468baa 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -165,13 +165,13 @@ static int get_parent_ino(struct inode *inode, nid_t *pino)
 {
        struct dentry *dentry;

-       inode = igrab(inode);
-       dentry = d_find_any_alias(inode);
-       iput(inode);
+       dentry = d_find_alias(inode);
        if (!dentry)
                return 0;

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