Tue, Sep 20, 2016 at 04:18:12PM CEST, eric.duma...@gmail.com wrote: >On Tue, 2016-09-20 at 07:11 -0700, Eric Dumazet wrote: >> On Tue, 2016-09-20 at 15:39 +0200, Jiri Pirko wrote: >> >> > I see. So how to silent the warning? >> > >> >> We can replace the atomic_add_return() and use a loop around >> atomic_read() and atomic_cmpxhg() >> >> This would change the nice property of x86 xadd into a loop. >> >> Or we also could fallback to random generation if the atomic_cmpxchg() >> fails. >> >> I'll provide a patch, thanks. >> > >Could you try the following ? > >diff --git a/net/ipv4/route.c b/net/ipv4/route.c >index >b52496fd51075821c39435f50ac62f813967aecc..91dc108ef6dc75df80f0e73b6fa062d98dc9a58a > 100644 >--- a/net/ipv4/route.c >+++ b/net/ipv4/route.c >@@ -476,12 +476,19 @@ u32 ip_idents_reserve(u32 hash, int segs) > atomic_t *p_id = ip_idents + hash % IP_IDENTS_SZ; > u32 old = ACCESS_ONCE(*p_tstamp); > u32 now = (u32)jiffies; >- u32 delta = 0; >+ u32 new, delta = 0; > > if (old != now && cmpxchg(p_tstamp, old, now) == old) > delta = prandom_u32_max(now - old); > >- return atomic_add_return(segs + delta, p_id) - segs; >+ old = (u32)atomic_read(p_id); >+ new = old + delta + segs; >+ /* Do not try too hard, if multiple cpus are there, >+ * just fallback to pseudo random number. >+ */ >+ if (unlikely(atomic_cmpxchg(p_id, old, new) != old)) >+ new = prandom_u32(); >+ return new; > } > EXPORT_SYMBOL(ip_idents_reserve); >
This patch makes ubsan silent. > >
