Hey,
Op 30-04-13 21:14, Daniel Vetter schreef:
On Sun, Apr 28, 2013 at 07:04:07PM +0200, Maarten Lankhorst wrote:
Changes since RFC patch v1:
- Updated to use atomic_long instead of atomic, since the reservation_id was a long.
- added mutex_reserve_lock_slow and mutex_reserve_lock_intr_slow
- removed mutex_locked_set_reservation_id (or w/e it was called)
Changes since RFC patch v2:
- remove use of __mutex_lock_retval_arg, add warnings when using wrong combination of mutex_(,reserve_)lock/unlock.
Changes since v1:
- Add __always_inline to __mutex_lock_common, otherwise reservation paths can be triggered from normal locks, because __builtin_constant_p might evaluate to false for the constant 0 in that case. Tests for this have been added in the next patch.
- Updated documentation slightly.
Changes since v2:
- Renamed everything to ww_mutex. (mlankhorst)
- Added ww_acquire_ctx and ww_class. (mlankhorst)
- Added a lot of checks for wrong api usage. (mlankhorst)
- Documentation updates. (danvet)
While writing the kerneldoc I've carefully check that all restrictions are enforced through debug checks somehow. I think that with full mutex debug (including lockdep) enabled, plus the slowpath injector patch I've just posted, _all_ interface abuse will be catched at runtime as long as all the single-threaded/uncontended cases are exercises sufficiently.
So I think we've fully achieved level 5 on the Rusty API safety scale here. Higher levels seem pretty hard given that the concepts are rather fancy, but I think with the new (and much more consitent) naming, plus the explicit introduction as (more abstruct) structures for ww_class and ww_acquire_context the interface is about as intuitive as it gets.
So all together I'm pretty happy with what the interface looks like. And one quick bikeshed below on the implementation. -Daniel
I included your fix below. I'm hoping to get this included in 3.11 through the drm tree, so I can convert ttm to use it, but I haven't received any further reply on the patch series.
The 3.10 mutex improvement patches don't seem to cause any conflicts when merging linus' tree, so I'll use drm-next as a base.
Are there any issues left? I included the patch you wrote for injecting -EDEADLK too in my tree. The overwhelming silence makes me think there are either none, or nobody cared enough to review it. :(
+/*
- after acquiring lock with fastpath or when we lost out in contested
- slowpath, set ctx and wake up any waiters so they can recheck.
- This function is never called when CONFIG_DEBUG_LOCK_ALLOC is set,
- as the fastpath and opportunistic spinning are disabled in that case.
- */
+static __always_inline void +ww_mutex_set_context_fastpath(struct ww_mutex *lock,
struct ww_acquire_ctx *ctx)+{
- unsigned long flags;
- struct mutex_waiter *cur;
- ww_mutex_lock_acquired(lock, ctx, false);
- lock->ctx = ctx;
- smp_mb__after_atomic_dec();
I think this should be
- smp_mb__after_atomic_dec();
- lock->ctx = ctx;
- smp_mb();
Also I wonder a bit how much this hurts the fastpath, and whether we should just shovel the ctx into the atomic field with a cmpxcht, like the rt mutex code does with the current pointer.
Fixed. I'm not sure if the second smp_mb is really needed. If there was a smp_mb__before_atomic_read it would have been sufficient.
~Maarten