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| author | Yuqi Jin <jinyuqi@huawei.com> | 2020-05-16 05:46:49 +0200 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2020-05-17 21:33:51 +0200 |
| commit | a6211caa634da39d861a47437ffcda8b38ef421b (patch) | |
| tree | 875f6cf4168b38a8f692d9ffb56c7920108c433b /net | |
| parent | dt-bindings: net: dsa: b53: Add missing size and address cells to example (diff) | |
| download | linux-a6211caa634da39d861a47437ffcda8b38ef421b.tar.xz linux-a6211caa634da39d861a47437ffcda8b38ef421b.zip | |
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>
Diffstat (limited to 'net')
| -rw-r--r-- | net/ipv4/route.c | 14 |
1 files changed, 6 insertions, 8 deletions
diff --git a/net/ipv4/route.c b/net/ipv4/route.c index fa829f31a3f5..b73f540fa19b 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); |