On 2019/5/10 下午12:48, Jason Wang wrote:
On 2019/5/10 上午10:59, Jason Wang wrote:
r = get_user_pages_fast(log, 1, 1, &page);
OK so the trick is that page is pinned so you don't expect
arch_futex_atomic_op_inuser below to fail. get_user_pages_fast
guarantees page is not going away but does it guarantee PTE won't be
invaidated or write protected?
Good point, then I think we probably need to do manual fixup through
fixup_user_fault() if arch_futex_atomic_op_in_user() fail.
This looks like a overkill, we don't need to atomic environment here
actually. Instead, just keep pagefault enabled should work. So just
introduce arch_futex_atomic_op_inuser_inatomic() variant with
pagefault disabled there just for futex should be sufficient.
Thanks
Ok, instead of using tricks, I think we can gracefully fallback to a
get_user()/put_user() pair protected by a mutex.
Let me post a non-rfc version for this.
Thanks
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