>What's the definition of a read memory barrier?
That's not the point. What you should tell me is that I can't reimplement
rmb() without a lock on the bus because the minium common divisor of a
spin_unlock() in pseudocode is not like in the Alpha implementation:
mb();
spinlock.lock = 0;
as I basically stated (I was thinking wrong) in my previous email.
On Alpha the spin_unlock can't be more finegrined because there's no way
you can _only_ avoid memory accesses before the barrier to be executed
after the barrier and letting accesses after the barrier to be executed
before the barrier.
I didn't understood well what IA32 enforces in a write: I thought the
write was enforcing order in both directions (up and down).
>---------
>AFAICS, the rmb() during set_current_state() is still required:
Not only the rmb() as it's common code (on i386 the rmb would be enough of
course). mb() is necessary instead.
BTW, In the example you provide below moving add_wait_queue in the middle
would remove the need of the barrier as an add_wait_queue executes both
the spin_lock and spin_unlock so it will sobstitute an mb() no matter how
the spin_lock/unlock are implemented.
>__wait_on_inode()
>add_wait_queue();
>current->state=TASK_UNINTERRUPTIBLE;
>if(inode->i_state & I_LOCK) {
> schedule();
Thanks.
Andrea
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