Re: [PATCH v8 4/4] qrwlock: Use smp_store_release() in write_unlock()

From: Linus Torvalds
Date: Sun Jan 19 2014 - 14:56:28 EST

On Sun, Jan 19, 2014 at 12:04 AM, Paul E. McKenney
<paulmck@xxxxxxxxxxxxxxxxxx> wrote:
> OK, another approach would be to never add "select ARCH_USE_QUEUE_RWLOCK"
> on Alpha, at least if the queued rwlocks really do want to atomically
> manipulate bytes. After all, the Alpha systems that I know about don't
> have enough CPUs to make queued rwlocks necessary anyway.
> Much simpler solution!
> Is this what you were getting at, or am I missing your point?

You're missing something.

Just make the "writer" field be an "int" on little-endian archiectures
(like alpha).

There is no reason for that field to be a "char" to begin with, as far
as I can tell, since the padding of the structure means that it
doesn't save any space. But even if that wasn't true, we could make an
arch-specific type for "minimum type for locking".

So my *point* was that it should be easy enough to just make sure that
any data structures used for locking have types that are appropriate
for that locking.

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