swap-make-each-swap-partition-have-one-address_space-fix-fix

swap-make-each-swap-partition-have-one-address_space-fix-fix

Sasha reported:
Commit "swap: make each swap partition have one address_space" is triggering
a series of warnings on boot:

[    3.446071] ------------[ cut here ]------------
[    3.446664] WARNING: at lib/debugobjects.c:261 debug_print_object+0x8e/0xb0()
[    3.447715] ODEBUG: init active (active state 0) object type: percpu_counter hint:           (null)
[    3.450360] Modules linked in:
[    3.451593] Pid: 1, comm: swapper/0 Tainted: G        W    3.8.0-rc4-next-20130124-sasha-00004-g838a1b4 #266
[    3.454508] Call Trace:
[    3.455248]  [<ffffffff8110d1bc>] warn_slowpath_common+0x8c/0xc0
[    3.455248]  [<ffffffff8110d291>] warn_slowpath_fmt+0x41/0x50
[    3.455248]  [<ffffffff81a2bb5e>] debug_print_object+0x8e/0xb0
[    3.455248]  [<ffffffff81a2c26b>] __debug_object_init+0x20b/0x290
[    3.455248]  [<ffffffff81a2c305>] debug_object_init+0x15/0x20
[    3.455248]  [<ffffffff81a3fbed>] __percpu_counter_init+0x6d/0xe0
[    3.455248]  [<ffffffff81231bdc>] bdi_init+0x1ac/0x270
[    3.455248]  [<ffffffff8618f20b>] swap_setup+0x3b/0x87
[    3.455248]  [<ffffffff8618f257>] ? swap_setup+0x87/0x87
[    3.455248]  [<ffffffff8618f268>] kswapd_init+0x11/0x7c
[    3.455248]  [<ffffffff810020ca>] do_one_initcall+0x8a/0x180
[    3.455248]  [<ffffffff86168cfd>] do_basic_setup+0x96/0xb4
[    3.455248]  [<ffffffff861685ae>] ? loglevel+0x31/0x31
[    3.455248]  [<ffffffff861885cd>] ? sched_init_smp+0x150/0x157
[    3.455248]  [<ffffffff86168ded>] kernel_init_freeable+0xd2/0x14c
[    3.455248]  [<ffffffff83cade10>] ? rest_init+0x140/0x140
[    3.455248]  [<ffffffff83cade19>] kernel_init+0x9/0xf0
[    3.455248]  [<ffffffff83d5727c>] ret_from_fork+0x7c/0xb0
[    3.455248]  [<ffffffff83cade10>] ? rest_init+0x140/0x140
[    3.455248] ---[ end trace 0b176d5c0f21bffb ]---

Initialize swap space backing_dev_info once to avoid the warning.

Signed-off-by: Shaohua Li <shli@fusionio.com>
Reported-by: Sasha Levin <sasha.levin@oracle.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>