On 07/08/2014 06:38 AM, Paul E. McKenney wrote: > From: "Paul E. McKenney" <paul...@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. Thanks, Lai -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
