Messages in this thread | | | Date | Mon, 23 Jan 2023 16:10:02 -0500 | Subject | Re: [PATCH v6 0/6] lockinig/rwsem: Fix rwsem bugs & enable true lock handoff | From | Waiman Long <> |
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On 1/22/23 22:40, Waiman Long wrote: > > On 1/22/23 08:46, Peter Zijlstra wrote: >> On Thu, Nov 17, 2022 at 09:20:10PM -0500, Waiman Long wrote: >> >>> Waiman Long (6): >>> locking/rwsem: Prevent non-first waiter from spinning in >>> down_write() slowpath >>> locking/rwsem: Disable preemption at all down_read*() and >>> up_read() code paths >>> locking/rwsem: Disable preemption at all down_write*() and >>> up_write() code paths >>> locking/rwsem: Change waiter->hanodff_set to a handoff_state enum >> After all these we still have down_read_non_owner() using >> __rwsem_set_reader_owner() outside of the preempt_disable() region. >> >> Now, let me go stare at this one: > > Thanks for spotting that. I kind of overlook the fact we have a > down_read_non_owner(). Will update that as well.
After looking further into this, we will need to either pass one more parameter to __down_read() for this special case or to do preempt_disable/enable in each of the higher level down_read functions. As down_read_non_owner() is a rarely called function, I doubt it is worth the extra effort to do that since the owner value (other than the RWSEM_READER_OWNED bit) is for debugging purpose only and is not critical to the correct functioning of a rwsem. I will add a comment to note that.
Cheers, Longman
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