Re: [PATCH linux-next] kernel/power: Use kmap_local_page() in snapshot.c

[chenguanxi11234]

What I've learned is that kmap_atomic() disables page-faults and 
preemption (the latter only for !PREEMPT_RT kernels).In my opinion, 
the code between the mapping and un-mapping in this patch does not 
depend on the above-mentioned side effects.So I simply replaced 
kmap_atomic() with kmap_local_page(). If I'm wrong, please explain it to me. 
Thank you.

>
>> Signed-off-by: Chen Haonan <chen.haonan2@xxxxxxxxxx>
>> ---
>>  kernel/power/snapshot.c | 12 ++++++------
>>  1 file changed, 6 insertions(+), 6 deletions(-)
>> diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
>> index 50a15408c3fc..feef0d4d3288 100644
>> --- a/kernel/power/snapshot.c
>> +++ b/kernel/power/snapshot.c
>> @@ -1487,11 +1487,11 @@ static bool copy_data_page(unsigned long dst_pfn, unsigned long src_pfn)
>>         s_page = pfn_to_page(src_pfn);
>>         d_page = pfn_to_page(dst_pfn);
>>         if (PageHighMem(s_page)) {
>> -               src = kmap_atomic(s_page);
>> -               dst = kmap_atomic(d_page);
>> +               src = kmap_local_page(s_page);
>> +               dst = kmap_local_page(d_page);
>>                 zeros_only = do_copy_page(dst, src);
>> -               kunmap_atomic(dst);
>> -               kunmap_atomic(src);
>> +               kunmap_local(dst);
>> +               kunmap_local(src);
>>         } else {
>>                 if (PageHighMem(d_page)) {
>>                         /*
>> @@ -1499,9 +1499,9 @@ static bool copy_data_page(unsigned long dst_pfn, unsigned long src_pfn)
>>                          * data modified by kmap_atomic()
>>                          */
>>                         zeros_only = safe_copy_page(buffer, s_page);
>> -                       dst = kmap_atomic(d_page);
>> +                       dst = kmap_local_page(d_page);
>>                         copy_page(dst, buffer);
>> -                       kunmap_atomic(dst);
>> +                       kunmap_local(dst);
>>                 } else {
>>                         zeros_only = safe_copy_page(page_address(d_page), s_page);
>>                 }
>> --
>> 2.25.1
>>