pidns: Make the pidns proc mount/umount logic obvious.

Track the number of pids in the proc hash table.  When the number of
pids goes to 0 schedule work to unmount the kernel mount of proc.

Move the mount of proc into alloc_pid when we allocate the pid for
init.

Remove the surprising calls of pid_ns_release proc in fork and
proc_flush_task.  Those code paths really shouldn't know about proc
namespace implementation details and people have demonstrated several
times that finding and understanding those code paths is difficult and
non-obvious.

Because of the call path detach pid is alwasy called with the
rtnl_lock held free_pid is not allowed to sleep, so the work to
unmounting proc is moved to a work queue.  This has the side benefit
of not blocking the entire world waiting for the unnecessary
rcu_barrier in deactivate_locked_super.

In the process of making the code clear and obvious this fixes a bug
reported by Gao feng <gaofeng@cn.fujitsu.com> where we would leak a
mount of proc during clone(CLONE_NEWPID|CLONE_NEWNET) if copy_pid_ns
succeeded and copy_net_ns failed.

Acked-by: "Serge E. Hallyn" <serge@hallyn.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

1 files changed, 0 insertions, 2 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index 7798c247f4b9..666dc8b06606 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1476,8 +1476,6 @@ bad_fork_cleanup_io:
         if (p->io_context)
                 exit_io_context(p);
 bad_fork_cleanup_namespaces:
-        if (unlikely(clone_flags & CLONE_NEWPID))
-                pid_ns_release_proc(p->nsproxy->pid_ns);
         exit_task_namespaces(p);
 bad_fork_cleanup_mm:
         if (p->mm)