[openib-general] Re: Re: ipoib_mcast_send.patch

[Michael S. Tsirkin]

Quoting r. Roland Dreier <rdreier at cisco.com>:
> Subject: Re: Re: ipoib_mcast_send.patch
> 
>     Michael> Right, but I thought atomic test_and_set_bit implied
>     Michael> smp_wmb already?
> 
> So did I but then I looked in the kernel source and now I think that
> set_bit operations are only ordered against other bitops that touch
> the same word.  For example ia64 just uses cmpxchg to implement the
> bitops, and powerpc just uses locked loads and stores.

Ugh, if thats the case you cant protect arbitrary data with
a bit: you need a spinlock or a barrier?
Wouldnt lots of code in ipoib that looks at bits be broken then?

-- 
Michael S. Tsirkin
Staff Engineer, Mellanox Technologies