[PATCH net v2 0/3] net: core: avoid unexpected situation in namespace change routine

[Taehee Yoo]

This patchset is to avoid an unexpected situation when an interface's
namespace is being changed.

When interface's namespace is being changed, dev_change_net_namespace()
is called. This removes and re-allocates many resources that include
sysfs files. The "/net/class/net/<interface name>" is one of them.
If the sysfs creation routine(device_rename()) found duplicate sysfs
file name, it warns about it and fails. But unfortunately, at that point,
dev_change_net_namespace() doesn't return fail because rollback cost
is too high.
So, the interface can't have a sysfs file.

The approach of this patchset is to find the duplicate sysfs file as
fast as possible. If it found that, dev_change_net_namespace() returns
fail immediately with zero rollback cost.

1. The first patch is to add class_has_file_ns() helper function.
   That function will be used for checking the existence of duplicate
   sysfs file.
2. The second patch is to add netdev_class_has_file_ns().
   That function is to check whether duplicate sysfs file in
   the "/sys/class/net*" using class_has_file_ns().
3. The last patch is to avoid an unexpected situation.
   a) If duplicate sysfs is existing, it fails as fast as possible in
      the dev_change_net_namespace()
   b) Acquire rtnl_lock() in both bond_create_sysfs() and
      bond_destroy_sysfs() to avoid race condition.
   c) Do not remove "/sys/class/net/bonding_masters" sysfs file by
      bond_destroy_sysfs() if the file wasn't created
      by bond_create_sysfs().

Test commands#1:
    ip netns add nst
    ip link add bonding_masters type dummy
    modprobe bonding
    ip link set bonding_masters netns nst

Test commands#2:
    ip link add bonding_masters type dummy
    ls /sys/class/net
    modprobe bonding
    modprobe -rv bonding
    ls /sys/class/net

After removing the bonding module, we can see the "bonding_masters"
interface's sysfs will be removed.
This is an unexpected situation.

Change log:
 - v1 -> v2:
   - Implement class_has_file_ns() instead of class_file_and_get_file_ns()
     in the first patch.
   - Change headline in the first patch.
   - Add kernel documentation comment in the first patch.
   - Use class_has_file_ns() in the second patch.
   - Change commit log in the third patch.

Taehee Yoo (3):
  class: add class_has_file_ns() helper function
  net: core: add netdev_class_has_file_ns() helper function
  net: core: avoid warning in dev_change_net_namespace()

 drivers/base/class.c             | 22 ++++++++++++++++++++++
 drivers/net/bonding/bond_sysfs.c | 13 ++++++++++++-
 include/linux/device/class.h     |  3 ++-
 include/linux/netdevice.h        |  2 +-
 include/net/bonding.h            |  1 +
 net/core/dev.c                   |  4 ++++
 net/core/net-sysfs.c             |  6 ++++++
 7 files changed, 48 insertions(+), 3 deletions(-)

-- 
2.17.1