evie/android_kernel_oneplus_msm8998
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

net: revert "net: get rid of an signed integer overflow in ip_idents_reserve()"

Browse source 
[ Upstream commit a6211caa634da39d861a47437ffcda8b38ef421b ]

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Yuqi Jin 2020-05-16 11:46:49 +08:00 • committed by Greg Kroah-Hartman
parent 450eda6db3
commit 6a14e9d237
1 changed files with 6 additions and 8 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

14
net/ipv4/route.c
View file

@ -477,18 +477,16 @@ u32 ip_idents_reserve(u32 hash, int segs)
atomic_t *p_id = ip_idents + hash % IP_IDENTS_SZ; atomic_t *p_id = ip_idents + hash % IP_IDENTS_SZ;
u32 old = ACCESS_ONCE(*p_tstamp); u32 old = ACCESS_ONCE(*p_tstamp);
u32 now = (u32)jiffies; u32 now = (u32)jiffies;
u32 new, delta = 0; u32 delta = 0;
if (old != now && cmpxchg(p_tstamp, old, now) == old) if (old != now && cmpxchg(p_tstamp, old, now) == old)
delta = prandom_u32_max(now - old); delta = prandom_u32_max(now - old);
/* Do not use atomic_add_return() as it makes UBSAN unhappy */ /* If UBSAN reports an error there, please make sure your compiler
do { * supports -fno-strict-overflow before reporting it that was a bug
old = (u32)atomic_read(p_id); * in UBSAN, and it has been fixed in GCC-8.
new = old + delta + segs; */
} while (atomic_cmpxchg(p_id, old, new) != old); return atomic_add_return(segs + delta, p_id) - segs;
return new - segs;
} }
EXPORT_SYMBOL(ip_idents_reserve); EXPORT_SYMBOL(ip_idents_reserve);