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
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