Messages in this thread | | | Date | Fri, 21 Oct 2022 09:44:23 +0200 (CEST) | From | Christoph Lameter <> | Subject | Re: [PATCH rcu 5/8] slab: Explain why SLAB_DESTROY_BY_RCU reference before locking |
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On Wed, 19 Oct 2022, Paul E. McKenney wrote:
> It is not obvious to the casual user why it is absolutely necessary to > acquire a reference to a SLAB_DESTROY_BY_RCU structure before acquiring > a lock in that structure. Therefore, add a comment explaining this point.
Sorry but this is not correct and difficult to comprehend.
1. You do not need a reference to a slab object after it was allocated. Objects must be properly protected by rcu_locks.
2. Locks are initialized once on slab allocation via a constructor (*not* on object allocation via kmem_cache_alloc)
3. Modifying locks at allocation/free is not possible since references to these objects may still persist after free and before alloc.
4. The old term SLAB_DESTROY_BY_RCU is used here.
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