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

Jaegeuk Kim
2020-05-05T18:49:35Z

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