• Kirill Tkhai's avatar
    net: Introduce net_rwsem to protect net_namespace_list · f0b07bb1
    Kirill Tkhai authored
    rtnl_lock() is used everywhere, and contention is very high.
    When someone wants to iterate over alive net namespaces,
    he/she has no a possibility to do that without exclusive lock.
    But the exclusive rtnl_lock() in such places is overkill,
    and it just increases the contention. Yes, there is already
    for_each_net_rcu() in kernel, but it requires rcu_read_lock(),
    and this can't be sleepable. Also, sometimes it may be need
    really prevent net_namespace_list growth, so for_each_net_rcu()
    is not fit there.
    
    This patch introduces new rw_semaphore, which will be used
    instead of rtnl_mutex to protect net_namespace_list. It is
    sleepable and allows not-exclusive iterations over net
    namespaces list. It allows to stop using rtnl_lock()
    in several places (what is made in next patches) and makes
    less the time, we keep rtnl_mutex. Here we just add new lock,
    while the explanation of we can remove rtnl_lock() there are
    in next patches.
    
    Fine grained locks generally are better, then one big lock,
    so let's do that with net_namespace_list, while the situation
    allows that.
    Signed-off-by: default avatarKirill Tkhai <ktkhai@virtuozzo.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    f0b07bb1
net_namespace.h 10.7 KB