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); > >
