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Date:   Tue, 5 May 2020 11:49:32 -0700
From:   Jaegeuk Kim <jaegeuk@kernel.org>
To:     Eric Biggers <ebiggers@kernel.org>
Cc:     linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net, kernel-team@android.com
Subject: Re: [f2fs-dev] [PATCH] f2fs: get parent inode when recovering pino
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 <20200505181941.GC98848@gmail.com>
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On 05/05, Eric Biggers wrote:
> 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@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;
> > 
> > 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@kernel.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@kernel.org>
> > Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.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.

Yeah, it seems to happen when open/rename/fsync calls, or race condition of
file deletion.

> 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;

How about this?

From 2a6b0e53e592854306062a2dc35db2d8f79062f2 Mon Sep 17 00:00:00 2001
From: Jaegeuk Kim <jaegeuk@kernel.org>
Date: Tue, 5 May 2020 11:33:29 -0700
Subject: [PATCH] f2fs: find a living dentry when finding parent ino

We need to check any dentry still alive to get parent inode number.

Suggested-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
---
 fs/f2fs/file.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index a0a4413d6083b..95139cb85faca 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -169,9 +169,8 @@ 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);
+	/* Need to check if valid dentry still exists. */
+	dentry = d_find_alias(inode);
 	if (!dentry)
 		return 0;
 
-- 
2.26.2.526.g744177e7f7-goog