Messages in this thread | | | Date | Thu, 9 Aug 2018 13:32:45 -0400 | From | "J. Bruce Fields" <> | Subject | Re: [PATCH 0/5 - V2] locks: avoid thundering-herd wake-ups |
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I think there's also a problem with multiple tasks sharing the same lock owner.
So, all locks are exclusive locks for the same range. We have four tasks. Tasks 1 and 4 share the same owner, the others' owners are distinct.
- Task 1 gets a lock. - Task 2 gets a conflicting lock. - Task 3 gets another conflicting lock. So now we the tree is 3->2->1. - Task 1's lock is released. - Before task 2 is scheduled, task 4 acquires a new lock. - Task 2 waits on task 4's lock, we now have 3->2->4.
Task 3 shouldn't be waiting--the lock it's requesting has the same owner as the lock task 4 holds--but we fail to wake up task 3.
--b.
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