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>

2 files changed, 0 insertions, 9 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 6177fc238fdb..7621dc51cff8 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2590,10 +2590,6 @@ void proc_flush_task(struct task_struct *task)
                 proc_flush_task_mnt(upid->ns->proc_mnt, upid->nr,
                                         tgid->numbers[i].nr);
         }
-
-        upid = &pid->numbers[pid->level];
-        if (upid->nr == 1)
-                pid_ns_release_proc(upid->ns);
 }
 
 static struct dentry *proc_pid_instantiate(struct inode *dir,
diff --git a/fs/proc/root.c b/fs/proc/root.c
index fc1609321a78..f2f251158d35 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -155,11 +155,6 @@ void __init proc_root_init(void)
         err = register_filesystem(&proc_fs_type);
         if (err)
                 return;
-        err = pid_ns_prepare_proc(&init_pid_ns);
-        if (err) {
-                unregister_filesystem(&proc_fs_type);
-                return;
-        }
 
         proc_self_init();
         proc_symlink("mounts", NULL, "self/mounts");