Remove the special case avoiding refcounting when the mm to be used is
the same as the kernel thread's active (lazy tlb) mm. kthread_use_mm()
should not be such a performance critical path that this matters much.
This simplifies a later change to lazy tlb mm refcounting.
Acked-by: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Nicholas Piggin <npig...@gmail.com>
---
kernel/kthread.c | 14 +++++---------
1 file changed, 5 insertions(+), 9 deletions(-)
diff --git a/kernel/kthread.c b/kernel/kthread.c
index f97fd01a2932..7424a1839e9a 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -1410,14 +1410,13 @@ void kthread_use_mm(struct mm_struct *mm)
WARN_ON_ONCE(!(tsk->flags & PF_KTHREAD));
WARN_ON_ONCE(tsk->mm);
+ mmgrab(mm);
+
task_lock(tsk);
/* Hold off tlb flush IPIs while switching mm's */
local_irq_disable();
active_mm = tsk->active_mm;
- if (active_mm != mm) {
- mmgrab(mm);
- tsk->active_mm = mm;
- }
+ tsk->active_mm = mm;
tsk->mm = mm;
membarrier_update_current_mm(mm);
switch_mm_irqs_off(active_mm, mm, tsk);
@@ -1434,12 +1433,9 @@ void kthread_use_mm(struct mm_struct *mm)
* memory barrier after storing to tsk->mm, before accessing
* user-space memory. A full memory barrier for membarrier
* {PRIVATE,GLOBAL}_EXPEDITED is implicitly provided by
- * mmdrop(), or explicitly with smp_mb().
+ * mmdrop().
*/
- if (active_mm != mm)
- mmdrop(active_mm);
- else
- smp_mb();
+ mmdrop(active_mm);
}
EXPORT_SYMBOL_GPL(kthread_use_mm);
--
2.37.2
