Messages in this thread | | | Date | Mon, 17 May 2010 14:06:06 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH RFC tip/core/rcu 23/23] vhost: add __rcu annotations |
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On Mon, May 17, 2010 at 11:33:49PM +0300, Michael S. Tsirkin wrote: > On Thu, May 13, 2010 at 08:23:40AM -0700, Paul E. McKenney wrote: > > On Thu, May 13, 2010 at 03:07:23PM +0200, Peter Zijlstra wrote: > > > On Wed, 2010-05-12 at 16:00 -0700, Paul E. McKenney wrote: > > > > Any thoughts? One approach would be to create a separate lockdep class > > > > for vhost workqueue state, similar to the approach used in instrument > > > > rcu_read_lock() and friends. > > > > > > workqueue_struct::lockdep_map, its held while executing worklets. > > > > > > lock_is_held(&vhost_workqueue->lockdep_map), should do as you want. > > > > Thank you, Peter!!! > > > > Thanx, Paul > > vhost in fact does flush_work rather than > flush_workqueue, so while for now everything runs > from vhost_workqueue in theory nothing would break > if we use some other workqueue or even a combination > thereof. > > I guess when/if this happens, we could start by converting > to _raw and then devise a solution.
If there are a small finite number of work queues involved, we can easily do something like:
#ifdef CONFIG_PROVE_RCU int in_vhost_workqueue(void) { return in_workqueue_context(vhost_workqueue) || in_workqueue_context(vhost_other_workqueue) || in_workqueue_context(yet_another_vhost_workqueue); } #endif /* #ifdef CONFIG_PROVE_RCU */
Seem reasonable?
> By the way what would be really nice is if we had a way > to trap when rcu protected pointer is freed without a flush > while some reader is running. Current annotation does not > allow this, does it?
Right now, it does not, but I wonder if something like Thomas's and Mathieu's debugobjects work could be brought to bear on this problem? This would need to be implemented in vhost, as synchronize_rcu() has no way to know what memory it is flushing, nor does flush_work().
Thanx, Paul
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