On Mon, May 27, 2013 at 10:26:39AM +0200, Maarten Lankhorst wrote: > Op 27-05-13 10:00, Peter Zijlstra schreef: > > 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? > > > It's easy to merge unlock_single and unlock, which I did in the next version > I'll post. > Lockdep will already warn if ww_mutex_lock and ww_mutex_lock_single are both > used. ww_test_block_context and ww_test_context_block in > lib/locking-selftest.c > are the testcases for this. > > The locking paths are too different, it will end up with doing "if (ctx == > NULL) mutex_lock(); else ww_mutex_lock();"
I was more thinking like: int __sched ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) { might_sleep(); return __mutex_lock_common(&lock->base, TASK_UNINTERRUPTIBLE, 0, ctx ? ctx->dep_map : NULL, _RET_IP_, ctx, 0); } That should make ww_mutex_lock(.ctx=NULL) equivalent to mutex_lock(&lock->base), no? Anyway, implementation aside, it would again reduce the interface some. -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html