On Tue, Jul 01, 2014 at 12:03:35PM +0200, Peter Zijlstra wrote:
> On Mon, Jun 30, 2014 at 11:49:40AM -0400, Jeff Layton wrote:
> > We currently have the ability to call lockdep_assert_held to throw a
> > warning when a spinlock isn't held in a codepath. There are also times
> > when we'd like to throw a warning when a lock is held (i.e. when there
> > is the potential for deadlock with atomic_dec_and_lock or similar).
> 
> So I'm not getting it; if there's deadlock potential, lockdep would
> already report so, right?
> 
> That is, lockdep is very good a yelling when you try to acquire a lock
> you're already holding.

Ah, I think I see what you're trying to do.

You're wanting to use might_lock() and might_lock_read(). Which are used
to make conditional lock acquisitions unconditional, so as to more
reliably trigger the deadlock detection.