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

Eric Biggers
2020-05-05T18:19:44Z

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.

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;