Messages in this thread | | | Date | Mon, 14 May 2018 06:34:03 -0700 | From | Christoph Hellwig <> | Subject | Re: [PATCH] nvme: fix lockdep warning in nvme_mpath_clear_current_path |
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On Mon, May 14, 2018 at 06:31:05AM -0700, Paul E. McKenney wrote: > > > + if (head && > > > + ns == rcu_dereference_protected(head->current_path, > > > + lockdep_is_held(&ns->ctrl->subsys->lock))) > > > rcu_assign_pointer(head->current_path, NULL); > > > } > > > struct nvme_ns *nvme_find_path(struct nvme_ns_head *head); > > > > We don't really dereference it at all in fact, but just check the > > pointers for equality. I wonder if there is a better way to do this, > > as my ANA patches add a caller without the lock (and withou SRU > > protection either now that I think of it) - for a pure pointer compare > > we really should not need any sort of protection. > > If you are just looking at the value of an RCU-protected pointer, then > using rcu_access_pointer() will cause RCU to just read out the value > and otherwise keeps its mouth shut.
That is exactly the function I was looking for. And given that srcu and rcu use the same annotations I should have through of being able to use it of course. As you see above we only use the return value to do a comparison, so we should be perfectly fine.
Johannes, can you respin the patch to use rcu_access_pointer?
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