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 <yang.s@xxxxxxxxxxxxxxx>
---
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
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