Messages in this thread | | | Date | Wed, 19 Sep 2007 14:49:56 -0400 | From | "Dmitry Torokhov" <> | Subject | Re: [RFC][PATCH 2/6] lockdep: validate rcu_dereference() vs rcu_read_lock() |
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On 9/19/07, Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote: > On Wed, Sep 19, 2007 at 10:32:49AM -0700, Paul E. McKenney wrote: > > On Wed, Sep 19, 2007 at 12:59:10PM -0400, Dmitry Torokhov wrote: > > > On 9/19/07, Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote: > > > > 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? > > > > > > Yes I do. Along with list_for_each_rcu(). > > > > OK, in that case it does indeed need to be handled. > > PS to previous -- any problem with inserting rcu_read_lock() and > rcu_read_unlock() around the portion of the IRQ handler that has > these accesses? >
I guess I could but it is an extra lock that needs to be managed and given the fact that it is not really needed (other to make a newly developed tool happy) I am hestsant to do that.
-- Dmitry - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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