Re: [PATCH 2/2] locking/rwsem: Disable optimistic spinning for PA-RISC
From: James Bottomley
Date: Fri Jun 06 2014 - 12:09:56 EST
On Fri, 2014-06-06 at 08:55 -0700, Davidlohr Bueso wrote:
> PA-RISC's cmpxchg is not save against normal stores and the code used
> for optimistic spinning is known broken because of this.
What about all the other identified architectures? The problem is that
unless you can do an atomic Read Modify Write on your architecture, you
have to implement our exchange primitives with locking, and that makes
you unsafe against stores We happen to be the architecture that
detected this, but I thought we agreed sparc32, metag, tile32, arc and
possibly hexagon have this problem.
Rather than naming all the failing architectures, we probably want an
ARCH_NO_ATOMIC_RMW
symbol which they select to indicate they can't do atomic exchange and
then you make
depends on SMP && RWSEM_XCHGADD_ALGORITHM &!ARCH_NO_ATOMIC_RMW
So they can all self select (especially if more come crawling out of the
woodwork).
James
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/