linux-ext4 - Re: [PATCH 6/6] fs: Restrict lock_two_nondirectories() to non-directory inodes

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Date:   Mon, 29 May 2023 14:42:08 +0200
From:   Jan Kara <jack@...e.cz>
To:     Amir Goldstein <amir73il@...il.com>
Cc:     Jan Kara <jack@...e.cz>, Al Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org,
        Christian Brauner <brauner@...nel.org>,
        Miklos Szeredi <miklos@...redi.hu>,
        "Darrick J. Wong" <djwong@...nel.org>, Ted Tso <tytso@....edu>,
        Jaegeuk Kim <jaegeuk@...nel.org>, linux-ext4@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net, linux-xfs@...r.kernel.org
Subject: Re: [PATCH 6/6] fs: Restrict lock_two_nondirectories() to
 non-directory inodes

On Fri 26-05-23 15:13:06, Amir Goldstein wrote:
> On Thu, May 25, 2023 at 1:17 PM Jan Kara <jack@...e.cz> wrote:
> >
> > Currently lock_two_nondirectories() is skipping any passed directories.
> > After vfs_rename() uses lock_two_inodes(), all the remaining four users
> > of this function pass only regular files to it. So drop the somewhat
> > unusual "skip directory" logic and instead warn if anybody passes
> > directory to it. This also allows us to use lock_two_inodes() in
> > lock_two_nondirectories() to concentrate the lock ordering logic in less
> > places.
> >
> > Signed-off-by: Jan Kara <jack@...e.cz>
> > ---
> >  fs/inode.c | 12 ++++--------
> >  1 file changed, 4 insertions(+), 8 deletions(-)
> >
> > diff --git a/fs/inode.c b/fs/inode.c
> > index 2015fa50d34a..accf5125a049 100644
> > --- a/fs/inode.c
> > +++ b/fs/inode.c
> > @@ -1140,7 +1140,7 @@ void lock_two_inodes(struct inode *inode1, struct inode *inode2,
> >  /**
> >   * lock_two_nondirectories - take two i_mutexes on non-directory objects
> >   *
> > - * Lock any non-NULL argument that is not a directory.
> > + * Lock any non-NULL argument. Passed objects must not be directories.
> >   * Zero, one or two objects may be locked by this function.
> >   *
> >   * @inode1: first inode to lock
> > @@ -1148,13 +1148,9 @@ void lock_two_inodes(struct inode *inode1, struct inode *inode2,
> >   */
> >  void lock_two_nondirectories(struct inode *inode1, struct inode *inode2)
> >  {
> > -       if (inode1 > inode2)
> > -               swap(inode1, inode2);
> > -
> > -       if (inode1 && !S_ISDIR(inode1->i_mode))
> > -               inode_lock(inode1);
> > -       if (inode2 && !S_ISDIR(inode2->i_mode) && inode2 != inode1)
> > -               inode_lock_nested(inode2, I_MUTEX_NONDIR2);
> > +       WARN_ON_ONCE(S_ISDIR(inode1->i_mode));
> > +       WARN_ON_ONCE(S_ISDIR(inode2->i_mode));
> > +       lock_two_inodes(inode1, inode2, I_MUTEX_NORMAL, I_MUTEX_NONDIR2);
> >  }
> >  EXPORT_SYMBOL(lock_two_nondirectories);
> >
> 
> Need the same treatment to unlock_two_nondirectories() because now if
> someone does pass a directory they will get a warning but also a leaked lock.

Yes, probably that is good defensive programming. I'll update the patch.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR