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


Kuniyuki Iwashima (10):
  net: fib_rules: Make fib_rules_ops.delete() return void.
  ipv4: fib_rules: Make the need for fib_unmerge() explicit.
  ipv4: fib: Protect fib_new_table() with spinlock.
  ipv4: fib: Drop RTNL annotation for net->ipv4.fib_table_hash[].
  net: fib_rules: Add fib_rules_ops.lock.
  net: fib_rules: Remove unnecessary EXPORT_SYMBOL.
  net: fib_rules: Drop RTNL assertions.
  net: fib_rules: Use dev_get_by_name_rcu().
  net: fib_rules: Only hold RTNL for the first IPv4 RTM_NEWRULE.
  ipv6: fib_rules: Convert fib6_rules_net_exit_rtnl() to ->exit().

 include/net/fib_rules.h  |  4 +-
 include/net/ip_fib.h     |  3 +-
 include/net/netns/ipv4.h |  1 +
 net/core/fib_rules.c     | 82 +++++++++++++++++++++-------------------
 net/ipv4/fib_frontend.c  | 48 ++++++++++++++++-------
 net/ipv4/fib_rules.c     | 20 ++++++----
 net/ipv4/fib_trie.c      |  3 +-
 net/ipv6/fib6_rules.c    | 17 ++-------
 8 files changed, 101 insertions(+), 77 deletions(-)

-- 
2.55.0.rc0.799.gd6f94ed593-goog