Messages in this thread | | | Subject | Re: [QUESTION] srcu: Remove the SCAN2 state | From | Byungchul Park <> | Date | Thu, 22 Feb 2018 14:05:18 +0900 |
| |
On 2/22/2018 11:11 AM, Paul E. McKenney wrote: > On Thu, Feb 22, 2018 at 08:57:27AM +0900, Byungchul Park wrote: >> Hello, >> >> I'm sorry for bothering you, and I seem to be obviously missing >> something, but I'm really wondering why we check try_check_zero() >> again in the state, SCAN1, for the previous srcu_idx. >> >> I mean, since we've already checked try_check_zero() in the previous >> grace period and gotten 'true' as a return value, all readers who see >> the flipped idx via srcu_flip() won't update the src_{lock,unlock}_count >> for the previous idx until it gets flipped back again. >> >> Is there any reasons we check try_check_zero() again in the state, SCAN1? >> Is there any problems if the following patch's applied? > > Indeed there are! Removing the second scan exposes us to a nasty race > condition where a reader is preempted (or interrupted or whatever) just
Indeed! I missed the cases. It should be as it is.
Thanks a lot for pointing it out.
> after fetching its counter. A detailed explanation for an essentially
-- Thanks, Byungchul
| |