Message ID | 1589600809-18001-1-git-send-email-zhangshaokun@hisilicon.com |
---|---|
State | Accepted |
Delegated to: | David Miller |
Headers | show |
Series | [v2] net: revert "net: get rid of an signed integer overflow in ip_idents_reserve()" | expand |
From: Shaokun Zhang <zhangshaokun@hisilicon.com> Date: Sat, 16 May 2020 11:46:49 +0800 > From: Yuqi Jin <jinyuqi@huawei.com> > > Commit adb03115f459 ("net: get rid of an signed integer overflow in ip_idents_reserve()") > used atomic_cmpxchg to replace "atomic_add_return" inside the function > "ip_idents_reserve". The reason was to avoid UBSAN warning. > However, this change has caused performance degrade and in GCC-8, > fno-strict-overflow is now mapped to -fwrapv -fwrapv-pointer > and signed integer overflow is now undefined by default at all > optimization levels[1]. Moreover, it was a bug in UBSAN vs -fwrapv > /-fno-strict-overflow, so Let's revert it safely. > > [1] https://gcc.gnu.org/gcc-8/changes.html > > Suggested-by: Peter Zijlstra <peterz@infradead.org> > Suggested-by: Eric Dumazet <edumazet@google.com> ... > Signed-off-by: Yuqi Jin <jinyuqi@huawei.com> > Signed-off-by: Shaokun Zhang <zhangshaokun@hisilicon.com> Applied, thanks.
diff --git a/net/ipv4/route.c b/net/ipv4/route.c index 788c69d9bfe0..455871d6b3a0 100644 --- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -491,18 +491,16 @@ u32 ip_idents_reserve(u32 hash, int segs) atomic_t *p_id = ip_idents + hash % IP_IDENTS_SZ; u32 old = READ_ONCE(*p_tstamp); u32 now = (u32)jiffies; - u32 new, delta = 0; + u32 delta = 0; if (old != now && cmpxchg(p_tstamp, old, now) == old) 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; + /* If UBSAN reports an error there, please make sure your compiler + * supports -fno-strict-overflow before reporting it that was a bug + * in UBSAN, and it has been fixed in GCC-8. + */ + return atomic_add_return(segs + delta, p_id) - segs; } EXPORT_SYMBOL(ip_idents_reserve);