Re: [RFC][PATCH 0/3] configfs: Make nested default groupslockdep-friendly
From: Arjan van de Ven
Date: Tue May 20 2008 - 18:14:22 EST
On Tue, 20 May 2008 14:56:39 -0700
Joel Becker <Joel.Becker@xxxxxxxxxx> wrote:
> On Tue, May 20, 2008 at 09:58:10AM -0700, Arjan van de Ven wrote:
> > On Tue, 20 May 2008 18:33:20 +0200
> > Louis Rilling <Louis.Rilling@xxxxxxxxxxx> wrote:
> > > The following patches fix lockdep warnings resulting from
> > > (correct) recursive locking in configfs.
> > >
> > > ...
> > >
> > > Since lockdep does not handle such correct recursion, the idea is
> > > to insert lockdep_off()/lockdep_on() for inode mutexes as soon as
> > > the level of recursion of the I_MUTEX_PARENT -> I_MUTEX_CHILD
> > > dependency pattern increases.
> > I'm... not entirely happy with such a solution ;(
> > there must be a better one.
> We're trying to find it. I really appreciate Louis taking the
> time to approach the issue. His first pass was to add 1 to
> MUTEX_CHILD for each level of recursion. This has a very tight limit
> (4 or 5 levels), but probably covers all users that exist and perhaps
> all that ever will exist. However, it means passing the lockdep
> annotation level throughout the entire call chain across multiple
> files. It was definitely less readable.
> This approach takes a different tack - it's very readable, but
> it assumes that the currently correct locking will always remain so -
> a particular invariant that lockdep exists to verify :-)
> Louis, what about sticking the recursion level on
> configfs_dirent? That is, you could add sd->s_level and then use it
> when needed. THis would hopefully avoid having to pass the level as
> an argument to every function. Then we can go back to your original
> scheme. If they recurse too much and hit the lockdep limit, just
> rewind everything and return -ELOOP.
you can also make a new lockdep key for each level... not pretty but it
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