On Thu, Nov 01, 2018 at 06:27:39PM +0100, Peter Zijlstra wrote:
> On Thu, Nov 01, 2018 at 06:14:32PM +0100, Peter Zijlstra wrote:
> > > This reminds me of this sooooo silly patch :/
> > >
> > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=adb03115f4590baa280ddc440a8eff08a6be0cb7
>
> You'd probably want to write it like so; +- some ordering stuff, that
> code didn't look like it really needs the memory barriers implied by
> these, but I didn't look too hard.
The atomic_fetch_add() API would need to be propagated out to the other
architectures, correct?
Thanx, Paul
> diff --git a/net/ipv4/route.c b/net/ipv4/route.c
> index c0a9d26c06ce..11deb1d7e96b 100644
> --- a/net/ipv4/route.c
> +++ b/net/ipv4/route.c
> @@ -485,16 +485,10 @@ u32 ip_idents_reserve(u32 hash, int segs)
> u32 now = (u32)jiffies;
> u32 new, delta = 0;
>
> - if (old != now && cmpxchg(p_tstamp, old, now) == old)
> + if (old != now && try_cmpxchg(p_tstamp, &old, now))
> delta = prandom_u32_max(now - old);
>
> - /* Do not use atomic_add_return() as it makes UBSAN unhappy */
> - do {
> - old = (u32)atomic_read(p_id);
> - new = old + delta + segs;
> - } while (atomic_cmpxchg(p_id, old, new) != old);
> -
> - return new - segs;
> + return atomic_fetch_add(segs + delta, p_id) + delta;
> }
> EXPORT_SYMBOL(ip_idents_reserve);
>
>
