mm/mmu_notifier: allocate mmu_notifier in advance

mm/mmu_notifier: allocate mmu_notifier in advance

While allocating mmu_notifier with parameter GFP_KERNEL, swap would start
to work in case of tight available memory.  Eventually, that would lead to
a deadlock while the swap deamon swaps anonymous pages.  It was caused by
commit e0f3c3f78da29b ("mm/mmu_notifier: init notifier if necessary").

: [49048.262912] =================================
: [49048.262913] [ INFO: inconsistent lock state ]
: [49048.262916] 3.7.0-rc1+ #518 Not tainted
: [49048.262918] ---------------------------------
: [49048.262919] inconsistent {RECLAIM_FS-ON-W} -> {IN-RECLAIM_FS-W} usage.
: [49048.262922] kswapd0/35 [HC0[0]:SC0[0]:HE1:SE1] takes:
: [49048.262924]  (&mapping->i_mmap_mutex){+.+.?.}, at: [<ffffffff81192fbc>] page_referenced+0x9c/0x2e0
: [49048.262933] {RECLAIM_FS-ON-W} state was registered at:
: [49048.262935]   [<ffffffff810ed5d6>] mark_held_locks+0x86/0x150
: [49048.262938]   [<ffffffff810edce7>] lockdep_trace_alloc+0x67/0xc0
: [49048.262942]   [<ffffffff811a9323>] kmem_cache_alloc_trace+0x33/0x230
: [49048.262945]   [<ffffffff811a1a27>] do_mmu_notifier_register+0x87/0x180
: [49048.262948]   [<ffffffff811a1b53>] mmu_notifier_register+0x13/0x20
: [49048.262951]   [<ffffffff81006738>] kvm_dev_ioctl+0x428/0x510
: [49048.262955]   [<ffffffff811c7ce8>] do_vfs_ioctl+0x98/0x570
: [49048.262959]   [<ffffffff811c8251>] sys_ioctl+0x91/0xb0
: [49048.262962]   [<ffffffff815df302>] system_call_fastpath+0x16/0x1b
: [49048.262966] irq event stamp: 825
: [49048.262968] hardirqs last  enabled at (825): [<ffffffff815d6fa0>] _raw_spin_unlock_irq+0x30/0x60
: [49048.262971] hardirqs last disabled at (824): [<ffffffff815d6659>] _raw_spin_lock_irq+0x19/0x80
: [49048.262975] softirqs last  enabled at (0): [<ffffffff81082170>] copy_process+0x630/0x17c0
: [49048.262979] softirqs last disabled at (0): [<          (null)>]           (null)
: ...

Simply back out the above commit, which was a small performance
optimization.

Signed-off-by: Gavin Shan <shangw@linux.vnet.ibm.com>
Reported-by: Andrea Righi <andrea@betterlinux.com>
Tested-by: Andrea Righi <andrea@betterlinux.com>
Cc: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Cc: Sagi Grimberg <sagig@mellanox.co.il>
Cc: Haggai Eran <haggaie@mellanox.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>