Messages in this thread | | | Date | Mon, 24 Oct 2022 15:31:17 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v3 2/5] locking/rwsem: Limit # of null owner retries for handoff writer |
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On Mon, Oct 17, 2022 at 05:13:53PM -0400, Waiman Long wrote: > Commit 91d2a812dfb9 ("locking/rwsem: Make handoff writer optimistically > spin on owner") assumes that when the owner field is changed to NULL, > the lock will become free soon. That assumption may not be correct > especially if the handoff writer doing the spinning is a RT task which > may preempt another task from completing its action of either freeing > the rwsem or properly setting up owner.
I'm confused again -- rwsem_*_owner() has lockdep_assert_preemption_disabled(). But more specifically; why can the RT task preempt a lock-op like that?
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