Messages in this thread | | | Date | Sat, 7 Mar 2015 10:21:26 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH] locking/rwsem: Fix lock optimistic spinning when owner is not running |
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On Fri, Mar 06, 2015 at 11:45:31PM -0800, Jason Low wrote: > static noinline > bool rwsem_spin_on_owner(struct rw_semaphore *sem, struct task_struct *owner) > { > long count; > > rcu_read_lock(); > + while (sem->owner == owner) { > + /* > + * Ensure we emit the owner->on_cpu, dereference _after_ > + * checking sem->owner still matches owner, if that fails, > + * owner might point to free()d memory, if it still matches, > + * the rcu_read_lock() ensures the memory stays valid. > + */ > + barrier(); > + > + /* abort spinning when need_resched or owner is not running */ > + if (!owner->on_cpu || need_resched()) { > rcu_read_unlock(); > return false; > }
Thanks, looks good; do we want to change the mutex code (again) to more closely resemble this too? It still has the while (true) instead of the while(lock->owner != owner).
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