linux-kernel - Re: [patch 06/14] hfsplus: remove hfsplus

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Message-Id: <E1JznjI-0003fD-9i@pomaz-ex.szeredi.hu>
Date:	Sat, 24 May 2008 08:59:48 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	zippel@...ux-m68k.org
CC:	miklos@...redi.hu, hch@...radead.org,
	linux-fsdevel@...r.kernel.org, viro@...IV.linux.org.uk,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 06/14] hfsplus: remove hfsplus_permission()

> > Semi-concrete: link(2) locks the target's parent and the source.
> > Cross-directory rename(2) locks both parents.  If link's target is a
> > file which has children, this can result in an ABBA deadlock.  That's
> > _before_ the filesystem's ->link() or ->rename() function is called.
> 
> I'm afraid you have to be more concrete than this. 
> hfsplus_file_inode_operations doesn't have a link or rename operation, so 
> if one your source parents above involves a file, it shouldn't get this 
> far or you have to describe your scenario in more detail.

Heh, you just want me to do all the hard work :)

OK, I'll go along:

  /mnt/a/x is a regular file

  ln /mnt/a/x /mnt/b/x
  rename /mnt/a/x /mnt/b/x/p & ln /mnt/b/x /mnt/a/q

Neither ->rename nor ->link is required to be defined on x.  The
rename will first lock x, then a.  The link will first lock a then x,
AFAICS.

This is probably just one of several ways to make it deadlock.

Hmm?

Miklos
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