Introduce `if_cloners_lock' rwlock and use it to serialize

if_clone_{create,destroy}(). This fixes the races described below.

if_clone_{create,destroy}() are kernel locked, but since they touch
various sleep points introduced by rwlocks and M_WAITOK allocations,
without serialization they can intersect due to race condition.

The avoided races are:

1. While performing if_clone_create(), concurrent thread which performing
    if_clone_create() can attach `ifp' with the same `if_xname' and made
    inconsistent `if_list' where all attached interfaces linked.
2. While performing if_clone_create(), concurrent thread which performing
    if_clone_destroy() can kill this incomplete `ifp'.
3. While performing if_clone_destroy(), concurrent thread which performing
    if_clone_destroy() can kill this dying `ifp'.


ok claudio@ kn@ mpi@ sashan@

0 files changed, 0 insertions, 0 deletions