Messages in this thread | | | Date | Wed, 19 Sep 2007 08:37:50 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [RFC][PATCH 2/6] lockdep: validate rcu_dereference() vs rcu_read_lock() |
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On Wed, Sep 19, 2007 at 11:16:21AM -0400, Dmitry Torokhov wrote: > On 9/19/07, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote: > > On Wed, 19 Sep 2007 10:17:25 -0400 "Dmitry Torokhov" > > <dmitry.torokhov@gmail.com> wrote: > > > > > Hi Peter, > > > > > > On 9/19/07, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote: > > > > Warn when rcu_dereference() is not used in combination with rcu_read_lock() > > > > > > > > > > According to Paul it is fine to use RCU primitives (when accompanied > > > with proper comments) when the read-size critical section is guarded > > > by spin_lock_irqsave()/spin_lock_irqsrestore() instead of > > > rcu_read_lock()/rcu_read_unlock() and writers synchronize with > > > synchronize_sched(), not synchronize_rcu(). Your patch will trigger > > > warnign on such valid usages. > > > > > > > Sounds fragile to begin with. But you're right in that that is valid > > for Linux as you know it. However in -rt most/all spinlocks are > > converted to sleeping locks. In that case sync_sched() is not enough. > > OK, then it goes beyond RCU... We need to come up with something that > can be used to synchronize with IRQ handlers (quite often in driver > code one needs to be sure that current invocation of IRQ handler > completed before doing something). And once we have it splinlock + RCU > users can just use that method.
But Peter's approach would not cause a problem here -- you wouldn't be doing an rcu_dereference from within the IRQ handler in this case, right?
That said, we will need something to handle threaded interrupts, since synchronize_sched() only waits for hardirq, NMI, SMI, etc., and not threaded IRQs.
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