net: revert "net: get rid of an signed integer overflow in ip_idents_reserve()"
authorYuqi Jin <jinyuqi@huawei.com>
Sat, 16 May 2020 03:46:49 +0000 (11:46 +0800)
committerDavid S. Miller <davem@davemloft.net>
Sun, 17 May 2020 19:33:51 +0000 (12:33 -0700)
commita6211caa634da39d861a47437ffcda8b38ef421b
tree875f6cf4168b38a8f692d9ffb56c7920108c433b
parent61d0301e6c05db55446c7c9b3b3294244649e7bc
net: revert "net: get rid of an signed integer overflow in ip_idents_reserve()"

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>
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>
net/ipv4/route.c