Merge branch 'net-fib_rules-rtnl-less-rtm_newrule-and-rtm_delrule'

Kuniyuki Iwashima says:

====================
net: fib_rules: RTNL-less RTM_NEWRULE and RTM_DELRULE.

RTM_NEWRULE and RTM_DELRULE acquire rtnl_net_lock(), but this is
only for fib_unmerge() in IPv4.

Since commit d954a67a7dfa ("ipv4: fib_rule: Move fib4_rules_exit()
to ->exit()."), RTM_DELRULE no longer needs RTNL.

fib_unmerge() is one-time event for each netns, so we only need
RTNL for the first IPv4 rule.

This series introduces per-fib_rules_ops mutex and drops RTNL
from fib_rules code except for the first IPv4 RTM_NEWRULE.

The script below creates 1K rules in parallel in 4K netns, and
it got 20x/30x faster for IPv4/IPv6.

  #!/bin/bash
  N=4096
  F=rules.txt

  for i in $(seq $N); do ip netns add ns-$i; done
  printf 'rule add from all table %d\n' {1..1024} > $F

  for v in 4 6; do
        echo "=== IPv${v} ==="
        time { for i in $(seq $N); do nsenter \
        --net=/var/run/netns/ns-$i ip -$v -batch $F & done; wait; }
  done

  for i in $(seq $N); do ip netns del ns-$i; done
  rm -f $F

Without this series:

  # ./test.sh
  === IPv4 ===

  real  0m22.752s
  user  0m7.834s
  sys   92m46.721s
  === IPv6 ===

  real  0m35.181s
  user  0m8.635s
  sys   142m30.479s

With this series:

  # ./test.sh
  === IPv4 ===

  real  0m0.918s
  user  0m5.675s
  sys   2m7.024s
  === IPv6 ===

  real  0m1.214s
  user  0m7.917s
  sys   4m19.489s
====================

Link: https://patch.msgid.link/20260629181226.1929658-1-kuniyu@google.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

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