netns: add pre_exit method to struct pernet_operations
Current struct pernet_operations exit() handlers are highly
discouraged to call synchronize_rcu().
There are cases where we need them, and exit_batch() does
not help the common case where a single netns is dismantled.
This patch leverages the existing synchronize_rcu() call
in cleanup_net()
Calling optional ->pre_exit() method before ->exit() or
->exit_batch() allows to benefit from a single synchronize_rcu()
call.
Note that the synchronize_rcu() calls added in this patch
are only in error paths or slow paths.
Tested:
$ time for i in {1..1000}; do unshare -n /bin/false;done
real 0m2.612s
user 0m0.171s
sys 0m2.216s
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2 files changed