On 14.11.2017 20:07, Eric Dumazet wrote: > On Tue, 2017-11-14 at 16:53 +0300, Kirill Tkhai wrote: >> Curently mutex is used to protect pernet operations list. It makes >> cleanup_net() to execute ->exit methods of the same operations set, >> which was used on the time of ->init, even after net namespace is >> unlinked from net_namespace_list. >> > ... > >> The solution is to convert net_mutex to the rw_semaphore. Then, >> pernet_operations::init/::exit methods, modifying the net-related data, >> will require down_read() locking only, while down_write() will be used >> for changing pernet_list. >> > ... > >> This patch requires commit 76f8507f7a64 "locking/rwsem: Add >> down_read_killable()" >> from Linus tree (not in net-next yet). > > > Looks great, thanks for doing this. > > I wonder if the down_read_killable() is really needed, maybe a > down_read() would not be blocking the thread too long after this change.
I'm afraid there are spin_unlock() or similar actions leading to preempt_enable(), which are made under the mutex/new rw_sem. They may be preempted and leave a cpu for some time. So the possibility to break the wait may be useful in some way...
