Re: [PATCH v4] x86/sgx: Fix the call order of synchronize_srcu() in sgx_release()

On 1/20/21 6:43 AM, Jarkko Sakkinen wrote:

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So why do you need the synchronize_srcu() call when this process sees an empty mm_list already?

Thx.

The other process aka some process using the enclave calls list_del_rcu() (and synchronize_srcu()), which starts a new grace period. If we don't do it, then the cleanup_srcu() will race with that grace period.

To me, this is only a partial explanation.

That goal of synchronize_srcu() is to wait for the completion of a *previous* grace period: one that might have observed the old state of the list.

Could you explain the *actual* effects of the misplaced synchronize_srcu()? If the race _occurs_, what is the side-effect?