* Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > PS: Ingo, why do the *_bh() functions in kernel/spinlock.c do > _both_ a "local_bh_disable()" and a "preempt_disable()"? BH > disable should disable preemption too, no? Or am I confused? In > which case we need that in the above rdlock_bh too. i think there might be (are?) uses of: spin_lock_bh(&some->lock); ... spin_unlock(&some->lock); ... local_bh_enable(); So we have to have two preemption control levels for that, as there's no knowledge at the spin_lock_bh() place whether it will be followed by a spin_unlock_bh() [in which case it would be safe to do SOFTIRQ_OFFSET only] - or by a spin_unlock() + local_bh_enable() pair.. [ That locking pattrn even makes a certain amount of sense: keep the lock held for a short amount of time - then weaken locking to bh context exclusion only. ] What we could do is an optimization to do a compound increase the preempt count by SOFTIRQ_OFFSET+1 - instead of a local_bh_disable() + preempt_disable()? Symmetrically we could do a compound decrease in the unlock case. It might even be called: local_bh_preempt_disable() or so? Ingo -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
