On 11/2/17 12:57 AM, Michal Hocko wrote:
> On Thu 02-11-17 05:38:33, Yang Shi wrote:
>> commit 3e51f3c4004c9b01f66da03214a3e206f5ed627b
>> ("sched/preempt: Remove PREEMPT_ACTIVE unmasking off in_atomic()") makes
>> in_atomic() just check the preempt count, so it is not necessary to use
>> preempt_count() in print_vma_addr() any more. Replace preempt_count() to
>> in_atomic() which is a generic API for checking atomic context.
>
> But why? Is there some general work to get rid of the direct preempt_count
> usage outside of the generic API?
I may not articulate it in the commit log, I would say "in_atomic" is
*preferred* API for checking atomic context instead of preempt_count()
which should be used for retrieving the preemption count value.
I would say there is not such general elimination work undergoing right
now, but if we go through the kernel code, almost everywhere "in_atomic"
is used for such use case already, except two places:
- print_vma_addr()
- debug_smp_processor_id()
Both came from Ingo long time ago before commit
3e51f3c4004c9b01f66da03214a3e206f5ed627b ("sched/preempt: Remove
PREEMPT_ACTIVE unmasking off in_atomic()"). But, after this commit was
merged, I don't see why *not* use in_atomic() to follow the convention.
Thanks,
Yang
>
>> Signed-off-by: Yang Shi <[email protected]>
>> ---
>> mm/memory.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/memory.c b/mm/memory.c
>> index a728bed..19b684e 100644
>> --- a/mm/memory.c
>> +++ b/mm/memory.c
>> @@ -4460,7 +4460,7 @@ void print_vma_addr(char *prefix, unsigned long ip)
>> * Do not print if we are in atomic
>> * contexts (in exception stacks, etc.):
>> */
>> - if (preempt_count())
>> + if (in_atomic())
>> return;
>>
>> down_read(&mm->mmap_sem);
>> --
>> 1.8.3.1
>
From 1582940311857173892@xxx Thu Nov 02 07:58:39 +0000 2017
X-GM-THRID: 1582901365152158645
X-Gmail-Labels: Inbox,Category Forums,HistoricalUnread