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net: revert "net: get rid of an signed integer overflow in ip_idents_reserve()"
[ Upstream commita6211caa63
] Commitadb03115f4
("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> Cc: "David S. Miller" <davem@davemloft.net> Cc: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru> Cc: Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org> Cc: Jakub Kicinski <kuba@kernel.org> Cc: Jiri Pirko <jiri@resnulli.us> Cc: Arvind Sankar <nivedita@alum.mit.edu> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Eric Dumazet <edumazet@google.com> Cc: Jiong Wang <jiongwang@huawei.com> Signed-off-by: Yuqi Jin <jinyuqi@huawei.com> Signed-off-by: Shaokun Zhang <zhangshaokun@hisilicon.com> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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1 changed files with 6 additions and 8 deletions
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@ -499,18 +499,16 @@ u32 ip_idents_reserve(u32 hash, int segs)
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atomic_t *p_id = ip_idents + hash % IP_IDENTS_SZ;
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u32 old = ACCESS_ONCE(*p_tstamp);
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u32 now = (u32)jiffies;
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u32 new, delta = 0;
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u32 delta = 0;
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if (old != now && cmpxchg(p_tstamp, old, now) == old)
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delta = prandom_u32_max(now - old);
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/* Do not use atomic_add_return() as it makes UBSAN unhappy */
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do {
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old = (u32)atomic_read(p_id);
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new = old + delta + segs;
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} while (atomic_cmpxchg(p_id, old, new) != old);
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return new - segs;
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/* If UBSAN reports an error there, please make sure your compiler
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* supports -fno-strict-overflow before reporting it that was a bug
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* in UBSAN, and it has been fixed in GCC-8.
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*/
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return atomic_add_return(segs + delta, p_id) - segs;
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}
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EXPORT_SYMBOL(ip_idents_reserve);
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