Messages in this thread | | | Date | Wed, 9 Jul 2014 09:04:20 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH tip/core/rcu 08/17] rcu: Allow post-unlock reference for rt_mutex |
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On Wed, Jul 09, 2014 at 09:50:09AM +0800, Lai Jiangshan wrote: > On 07/08/2014 06:38 AM, Paul E. McKenney wrote: > > From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> > > > > The current approach to RCU priority boosting uses an rt_mutex strictly > > for its priority-boosting side effects. The rt_mutex_init_proxy_locked() > > function is used by the booster to initialize the lock as held by the > > boostee. The booster then uses rt_mutex_lock() to acquire this rt_mutex, > > which priority-boosts the boostee. When the boostee reaches the end > > of its outermost RCU read-side critical section, it checks a field in > > its task structure to see whether it has been boosted, and, if so, uses > > rt_mutex_unlock() to release the rt_mutex. The booster can then go on > > to boost the next task that is blocking the current RCU grace period. > > > > But reasonable implementations of rt_mutex_unlock() might result in the > > boostee referencing the rt_mutex's data after releasing it. > > XXXX_unlock(lock_ptr) should not reference to the lock_ptr after it has unlocked the lock. (*) > So I think this patch is unneeded. Although its adding overhead is at slow-patch, > but it adds REVIEW-burden. > > And although the original rt_mutex_unlock() violates the rule(*) when the fast-cmpxchg-path, > but it is fixed now. > > It is the lock-subsystem's responsible to do this. I prefer to add the wait_for_complete() > stuff until the future when the boostee needs to re-access the booster after rt_mutex_unlock() > instead of now.
It is on my list to remove. ;-)
Thanx, Paul
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