On 05/12/2010 05:55 PM, Linus Torvalds wrote:
Wouldn't it be sufficient to do
if (atomic_dec_and_test(&anon_vma->ksm_refcount)) {
anon_vma_lock(anon_vma);
instead? The "atomic_dec_and_lock()" semantics are _much_ stricter than a
regular "decrement and test and then lock", and that strictness means that
it's way more complicated and expensive. So if you don't need the
semantics, you shouldn't use them.
I suspect the atomic_dec_and_lock in the KVM code is being used
to prevent the following race:
1) KSM code reduces the refcount to 0
2) munmap on other CPU frees the anon_vma
3) KSM code takes the anon_vma lock,
which now lives in freed memory
Am I totally confused by this and can we use a nicer approach?
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