[PATCH v3 2/3] mutex: add support for wound/wait style locks, v3

[Peter Zijlstra]

On Wed, May 22, 2013 at 07:24:38PM +0200, Maarten Lankhorst wrote:
> >> +- Functions to only acquire a single w/w mutex, which results in the exact same
> >> +  semantics as a normal mutex. These functions have the _single postfix.
> > This is missing rationale.

> trylock_single is useful when iterating over a list, and you want to evict a bo, but only the first one that can be acquired.
> lock_single is useful when only a single bo needs to be acquired, for example to lock a buffer during mmap.

OK, so given that its still early, monday and I haven't actually spend
much time thinking on this; would it be possible to make:
ww_mutex_lock(.ctx=NULL) act like ww_mutex_lock_single()?

The idea is that if we don't provide a ctx, we'll get a different
lockdep annotation; mutex_lock() vs mutex_lock_nest_lock(). So if we
then go and make a mistake, lockdep should warn us.

Would that work or should I stock up on morning juice?