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

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Date:   Tue, 5 May 2020 11:13:23 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Eric Biggers <ebiggers@...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 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;
-- 
2.26.2.526.g744177e7f7-goog