The cpuacct split caused this build failure on UML:

  kernel/sched/cpuacct.c:94:2: error: implicit declaration of  function 'ERR_PTR'

Cc: Li Zefan <lizefan@huawei.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

Now we're guaranteed when cpuacct_charge() and
cpuacct_account_field() are called, cpuacct has already been
properly initialized, so we no longer need those checks.
Signed-off-by: NLi Zefan <lizefan@huawei.com>
Cc: Tejun Heo <tj@kernel.org>
Acked-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/5155384C.7000508@huawei.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

Initialize cpuacct before the scheduler is functioning, so when
cpuacct_charge() and cpuacct_account_field() are called,
task_ca() won't return NULL.
Signed-off-by: NLi Zefan <lizefan@huawei.com>
Cc: Tejun Heo <tj@kernel.org>
Acked-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/5155383F.8000005@huawei.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

Now we don't need cpuacct_init(), and instead we just initialize
root_cpuacct when it's defined.
Signed-off-by: NLi Zefan <lizefan@huawei.com>
Cc: Tejun Heo <tj@kernel.org>
Acked-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/51553834.9090701@huawei.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

This is a preparation, so later we can initialize cpuacct
earlier.
Signed-off-by: NLi Zefan <lizefan@huawei.com>
Cc: Tejun Heo <tj@kernel.org>
Acked-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/51553822.5000403@huawei.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

Now most of the code in cpuacct.h can be moved to cpuacct.c
Signed-off-by: NLi Zefan <lizefan@huawei.com>
Acked-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/515536D5.2080401@huawei.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

This is a micro optimazation for a hot path.

- We don't need to check if @CA returned from task_ca() is NULL.
- We don't need to check if @CA returned from parent_ca() is NULL.
Signed-off-by: NLi Zefan <lizefan@huawei.com>
Acked-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/515536B7.6060602@huawei.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

This is a micro optimization for the hot path.

- We don't need to check if @CA is NULL in parent_ca().
- We don't need to check if @CA is NULL in the beginning of the for loop.
Signed-off-by: NLi Zefan <lizefan@huawei.com>
Acked-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/515536A9.5000700@huawei.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

So we can remove open-coded cpuacct code in cputime.c.
Signed-off-by: NLi Zefan <lizefan@huawei.com>
Acked-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/51553692.9060008@huawei.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

So we don't open-coded initialization of cpuacct in core.c.
Signed-off-by: NLi Zefan <lizefan@huawei.com>
Acked-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/51553687.1060906@huawei.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

Signed-off-by: NLi Zefan <lizefan@huawei.com>
Acked-by: NPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/5155366F.5060404@huawei.comSigned-off-by: NIngo Molnar <mingo@kernel.org>