schedule()
                                        |      -> move charge should wake it up

This patch fixes all of these problems by:
1. revert the commit.
2. To fix the Ex.1, we set mc.moving_task after mem_cgroup_count_precharge()
   has released the mmap_sem.
3. To fix the Ex.2, we use down_read_trylock() instead of down_read() in
   mem_cgroup_move_charge() and, if it has failed to aquire the lock, cancel
   all extra charges, wake up all waiters, and retry trylock.

Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Reported-by: Ben Blum <bblum@andrew.cmu.edu>
Cc: Miao Xie <miaox@cn.fujitsu.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Paul Menage <menage@google.com>
Cc: Hiroyuki Kamezawa <kamezawa.hiroyuki@gmail.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
=Ê