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    SubjectRe: [PATCH RFC 00/25] Replacing net_mutex with rw_semaphore
    Kirill Tkhai <ktkhai@virtuozzo.com> writes:

    > Hi,
    >
    > this is continuation of discussion from here:
    >
    > https://lkml.org/lkml/2017/11/14/298
    >
    > The plan has changed a little bit, so I'd be happy to hear
    > people's comments, before I dived into all 400+ pernet subsys
    > and devices.
    >
    > The patch set adds pernet sys list ahead of subsys and device,
    > and it's used for pernet_operations, which may be executed
    > in parallel with any other pernet_operations methods. Also,
    > some high-priority ops converted (up to registered using
    > postcore_initcall(), and some subsys_initcall()) in order
    > of appearance. The sequence in setup_net() is following:
    >
    > 1)execute all the callbacks from pernet_sys list
    > 2)lock net_mutex
    > 3)execute all the callbacks from pernet_subsys list
    > 4)execute all the callbacks from pernet_device list
    > 5)unlock net_mutex
    >
    > There was not pernet_operations, requiring additional
    > synchronization, yet, but I've bumped in another problem.
    > The problem is that some drivers may be compiled as modules
    > and as kernel-image part. They register pernet_operations
    > from device_initcall() for example. This initcall executes
    > in different time comparing to in-kernel built-in only
    > drivers.
    >
    > Imagine, we have three state driverA, and boolean driverB.
    > driverA registers pernet_subsys from subsys_initcall().
    > driverB registers pernet_subsys from fs_initcall().
    > So, here we have two cases:
    >
    > driverA is module driverA is built-in
    > -------------------- -------------------
    > register driverB ops register driverA ops
    > register driverA ops register driverB ops
    >
    > So, the order is different. When converting driver one-by-one,
    > it's impossible to make the order true for all .config
    > states, because of the above. So, the bisect won't work.
    >
    > And it seems, it's just the same as to convert pernet_operations
    > from all the files in file alphabetical order. What do you
    > think about this? (Note, the patches has no such a problem
    > at the moment, as there are all in-kernel early core drivers).
    >
    > Maybe there are another comments on the code.

    I think there is an solution in the center. Just have a count
    (protected by down_write net_sem) of the number of modules that still
    need net_mutex.

    If the count is non-zero we take net_mutex in setup_net and cleanup_net.

    That way limited network stacks can see the benefit and actively test
    the parallism, while other configurations can be safe in still having
    the same behavior.

    Eric


    > ---
    >
    > Kirill Tkhai (25):
    > net: Assign net to net_namespace_list in setup_net()
    > net: Cleanup copy_net_ns()
    > net: Introduce net_sem for protection of pernet_list
    > net: Move mutex_unlock() in cleanup_net() up
    > net: Add primitives to update heads of pernet_list sublists
    > net: Add pernet sys and registration functions
    > net: Make sys sublist pernet_operations executed out of net_mutex
    > net: Move proc_net_ns_ops to pernet_sys list
    > net: Move net_ns_ops to pernet_sys list
    > net: Move sysctl_pernet_ops to pernet_sys list
    > net: Move netfilter_net_ops to pernet_sys list
    > net: Move nf_log_net_ops to pernet_sys list
    > net: Move net_inuse_ops to pernet_sys list
    > net: Move net_defaults_ops to pernet_sys list
    > net: Move netlink_net_ops to pernet_sys list
    > net: Move rtnetlink_net_ops to pernet_sys list
    > net: Move audit_net_ops to pernet_sys list
    > net: Move uevent_net_ops to pernet_sys list
    > net: Move proto_net_ops to pernet_sys list
    > net: Move pernet_subsys, registered via net_dev_init(), to pernet_sys list
    > net: Move fib_* pernet_operations, registered via subsys_initcall(), to pernet_sys list
    > net: Move subsys_initcall() registered pernet_operations from net/sched to pernet_sys list
    > net: Move genl_pernet_ops to pernet_sys list
    > net: Move wext_pernet_ops to pernet_sys list
    > net: Move sysctl_core_ops to pernet_sys list
    >
    >
    > fs/proc/proc_net.c | 2
    > include/linux/rtnetlink.h | 1
    > include/net/net_namespace.h | 2
    > kernel/audit.c | 2
    > lib/kobject_uevent.c | 2
    > net/core/dev.c | 2
    > net/core/fib_notifier.c | 2
    > net/core/fib_rules.c | 2
    > net/core/net-procfs.c | 4 -
    > net/core/net_namespace.c | 203 +++++++++++++++++++++++++++++++++----------
    > net/core/rtnetlink.c | 6 +
    > net/core/sock.c | 4 -
    > net/core/sysctl_net_core.c | 2
    > net/netfilter/core.c | 2
    > net/netfilter/nf_log.c | 2
    > net/netlink/af_netlink.c | 2
    > net/netlink/genetlink.c | 2
    > net/sched/act_api.c | 2
    > net/sched/sch_api.c | 2
    > net/sysctl_net.c | 2
    > net/wireless/wext-core.c | 2
    > 21 files changed, 183 insertions(+), 67 deletions(-)
    >
    > --
    > Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>

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