On 09/14/2009 01:49 AM, Marcelo Tosatti wrote:
I think synchronize_srcu() will be deferred until the fault path is
complete (and srcu_read_unlock() runs). Copying someone who knows for
sure.
Yes, synchronize_srcu() will block until srcu_read_unlock() in this
scenario, assuming that the same srcu_struct is used by both.
Right it will. But this does not stop the fault path from creating
shadow pages with stale sp->gfn (the only way to do that would be mutual
exclusion AFAICS).
So we put the kvm_mmu_zap_pages() call as part of the synchronize_srcu()
callback to take advantage of the srcu guarantees. We know that when
when the callback is called all new reads see the new slots and all old
readers have completed.
The RCU read-protected side does not stop a new memslots pointer from
being assigned (with rcu_assign_pointer), does it?
It doesn't. It only gives you a point in time where you know no one is
using the old pointer, but before it has been deleted.
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
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