Re: rw_semaphores

[Linus Torvalds]

On Tue, 10 Apr 2001, Tachino Nobuhiro wrote:
>
>   I am not familiar with semaphore or x86, so this may not be correct,
> but if the following sequence is possible, the writer can call wake_up()
> before the reader calls add_wait_queue() and reader may sleep forever.
> Is it possible?

The ordering is certainly possible, but if it happens,
__down_read_failed() won't actually sleep, because it will notice that the
value is positive and just return immediately. So it will do some
unnecessary work (add itself to the wait-queue only to remove itself
immediately again), but it will do the right thing.

		Linus