Messages in this thread | | | Date | Tue, 27 Feb 2007 15:13:15 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH] adapt page_lock_anon_vma() to PREEMPT_RCU |
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On Tue, Feb 27, 2007 at 12:25:17PM -0800, Andrew Morton wrote: > > On Sun, 25 Feb 2007 23:06:21 +0300 Oleg Nesterov <oleg@tv-sign.ru> wrote: > > page_lock_anon_vma() uses spin_lock() to block RCU. This doesn't work with > > PREEMPT_RCU, we have to do rcu_read_lock() explicitely. Otherwise, it is > > theoretically possible that slab returns anon_vma's memory to the system > > before we do spin_unlock(&anon_vma->lock). > > > > ... > > > > +static void page_unlock_anon_vma(struct anon_vma *anon_vma) > > +{ > > + spin_unlock(&anon_vma->lock); > > + rcu_read_unlock(); > > } > > It's a bit sad doing a double preempt_disable() for non-PREEMPT_RCU builds. > > Perhaps we would benefit from a new rcu_read_lock_preempt_rcu() which is a > no-op if !PREEMPT_RCU.
We were doing double preempt_disable() before as well. The only difference is that we moved RCU preempt_enable() (it used to be inside the critical section, and now it is after the corresponding spin_unlock()).
I hope to keep RCU API proliferation down to a dull roar, but if we need more APIs, we need more APIs. This example does not demonstrate that need to me, however.
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