Re: [PATCH v2 4/6] fs: Establish locking order for unrelated directories

From: Jan Kara <jack@suse.cz>
To: Christian Brauner <brauner@kernel.org>
Cc: Jan Kara <jack@suse.cz>, Al Viro <viro@ZenIV.linux.org.uk>,
	linux-fsdevel@vger.kernel.org, Miklos Szeredi <miklos@szeredi.hu>,
	"Darrick J. Wong" <djwong@kernel.org>, Ted Tso <tytso@mit.edu>,
	Jaegeuk Kim <jaegeuk@kernel.org>,
	linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org,
	linux-f2fs-devel@lists.sourceforge.net, stable@vger.kernel.org
Subject: Re: [PATCH v2 4/6] fs: Establish locking order for unrelated directories
Date: Thu, 1 Jun 2023 17:24:49 +0200	[thread overview]
Message-ID: <20230601152449.h4ur5zrfqjqygujd@quack3> (raw)
In-Reply-To: <20230601-gebracht-gesehen-c779a56b3bf3@brauner>

On Thu 01-06-23 15:58:58, Christian Brauner wrote:
> On Thu, Jun 01, 2023 at 12:58:24PM +0200, Jan Kara wrote:
> > Currently the locking order of inode locks for directories that are not
> > in ancestor relationship is not defined because all operations that
> > needed to lock two directories like this were serialized by
> > sb->s_vfs_rename_mutex. However some filesystems need to lock two
> > subdirectories for RENAME_EXCHANGE operations and for this we need the
> > locking order established even for two tree-unrelated directories.
> > Provide a helper function lock_two_inodes() that establishes lock
> > ordering for any two inodes and use it in lock_two_directories().
> > 
> > CC: stable@vger.kernel.org
> > Signed-off-by: Jan Kara <jack@suse.cz>
> > ---
> >  fs/inode.c    | 42 ++++++++++++++++++++++++++++++++++++++++++
> >  fs/internal.h |  2 ++
> >  fs/namei.c    |  4 ++--
> >  3 files changed, 46 insertions(+), 2 deletions(-)
> > 
> > diff --git a/fs/inode.c b/fs/inode.c
> > index 577799b7855f..4000ab08bbc0 100644
> > --- a/fs/inode.c
> > +++ b/fs/inode.c
> > @@ -1103,6 +1103,48 @@ void discard_new_inode(struct inode *inode)
> >  }
> >  EXPORT_SYMBOL(discard_new_inode);
> >  
> > +/**
> > + * lock_two_inodes - lock two inodes (may be regular files but also dirs)
> > + *
> > + * Lock any non-NULL argument. The caller must make sure that if he is passing
> > + * in two directories, one is not ancestor of the other.  Zero, one or two
> > + * objects may be locked by this function.
> > + *
> > + * @inode1: first inode to lock
> > + * @inode2: second inode to lock
> > + * @subclass1: inode lock subclass for the first lock obtained
> > + * @subclass2: inode lock subclass for the second lock obtained
> > + */
> > +void lock_two_inodes(struct inode *inode1, struct inode *inode2,
> > +		     unsigned subclass1, unsigned subclass2)
> > +{
> > +	if (!inode1 || !inode2)
> 
> I think you forgot the opening bracket...
> I can just fix this up for you though.

Oh, yes. Apparently I forgot to rerun git-format-patch after fixing up this
bit. I'm sorry for that. The patch series has survived full ext4 fstests
run on my end.

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