Probably all of you know about "lock inversion". There was a similar
problem on restoring pipes.

One process try to restore pipe1 and waits when another process attached
to it.  In this time another process restores pipe2 and waits too.

I know two solves.
1. Open all pipes -> attach to them -> close unnecessary ends.
This method has a problem, if only one end belongs to the process.  In
this cases another end occupies a descriptor, which may be needed to
another pipe.

2. Restore pipes in the same order. This patch does that.
A sorted list of pipe entries are constructed.
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Acked-by: Pavel Emelianov <xemul@parallels.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>