Re: UBSAN reports issue in ip_idents_reserve
flat view
From: Eric Dumazet <hidden>
Date: 2016-09-20 14:18:15
Subsystem:
networking [general], networking [ipv4/ipv6], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, David Ahern, Ido Schimmel, Linus Torvalds
On Tue, 2016-09-20 at 07:11 -0700, Eric Dumazet wrote:
On Tue, 2016-09-20 at 15:39 +0200, Jiri Pirko wrote:quoted
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.cindex 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);