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

[Fred Kimmy]

[Bug Description]
There is an significant performance regression with the following
commit-id <adb03115f459>
("net: get rid of an signed integer overflow in ip_idents_reserve()").

Both on x86 server(Skylake) and ARM64 server, when cpu core number
increase, the function ip_idents_reserve() of cpu usage is very high,
and the performance will become bad. After revert the patch, we can
avoid this problem when cpu core number increases.

With the patch on x86, ip_idents_reserve() cpu usage is 63.05% when
iperf3 is run with 32 cpu cores.
Samples: 18K of event 'cycles:ppp', Event count (approx.)
  Children Self Command Shared Object Symbol
    63.18% 63.05% iperf3 [kernel.vmlinux] [k] ip_idents_reserve

And the IOPS is 4483830pps.
10:46:13 AM IFACE rxpck/s txpck/s rxkB/s txkB/s
10:46:14 AM lo 4483830.00 4483830.00 192664.57 192664.57

Resert the patch, ip_idents_reserve() cpu usage is 17.05%.
Samples: 37K of event 'cycles:ppp', 4000 Hz, Event count (approx.)
  Children Self Shared Object Symbol
    17.07% 17.05% [kernel] [k] ip_idents_reserve

And the IOPS is 1160021pps.
05:03:15 PM IFACE rxpck/s txpck/s rxkB/s txkB/s
05:03:16 PM lo 11600213.00 11600213.00 498446.65 498446.65

[Steps to Reproduce]
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[Actual Results]

[Expected Results]

[Reproducibility]

[Additional information]
  (Firmware version, kernel version, affected hardware, etc. if required):

[Resolution]
[Bug Description]
 hns3 patchset have merged into mainline 5.7rc6 kernel.

[Steps to Reproduce]
  1)
  2)
  3)

[Actual Results]

[Expected Results]

[Reproducibility]

[Additional information]
  (Firmware version, kernel version, affected hardware, etc. if required):

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

[Ike Panhc (ikepanhc)]

a6211caa634d net: revert "net: get rid of an signed integer overflow in ip_idents_reserve()"

This patch has been merged into mainline kernel since 5.7-rc7

[Ike Panhc (ikepanhc)]

We have the original patch applied into ubuntu-focal.

ubuntu-focal$ gitoneline | grep 'ip_idents_reserve'
adb03115f459 <email address hidden> 2016-09-22 02:41:17 -0400 net: get rid of an signed integer overflow in ip_idents_reserve()

and we need to find out if there is an revised patch to fix the overflow.

[dann frazier (dannf)]

We have already reverted the patch as part of merging v5.4.44:
https://kernel.ubuntu.com/git/ubuntu/ubuntu-focal.git/commit/?id=409d1d5f5a1537d02668e97ad0e316244cc14e3e

[Ike Panhc (ikepanhc)]

In bionic hwe kernel as 5.3.0-63.57~18.04.1 too. Expect to hit -update 20th July