Re: [PATCH v2 4/5] mm: make vma cache SLAB_TYPESAFE_BY_RCU

[Hugh Dickins]

On Tue, 12 Nov 2024, Suren Baghdasaryan wrote:
> 
> Thinking about this some more, I don't think this works. I'm relying
> on vma_start_read() to stabilize the vma, however the lock I'm taking
> is part of the vma which can be reused from under us. So, the lock I'm
> taking might be reinitialized after I take the lock...
> I need to figure out a way to stabilize the vma in some other manner
> before taking this lock.

(I'm not paying attention and following the patches, I just happened
to notice this remark: forgive me if I'm out of context and have
misunderstood, but hope this might help:)

But this is exactly the problem SLAB_TYPESAFE_BY_RCU was invented for.
You just have to be careful that the locks are initialized only when the
slab is first created (allocated from buddy), not reinitialized whenever
a new object is allocated from that slab.

Hugh