[RFC PATCH 3/7] mm: introduce exit_lazy_tlb

Nicholas Piggin
2020-07-10T01:57:24Z

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
fs/exec.c | 5 +++--
include/asm-generic/mmu_context.h | 20 ++++++++++++++++++++
kernel/kthread.c | 1 +
kernel/sched/core.c | 2 ++
4 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index e6e8a9a70327..e2ab71e88293 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1117,9 +1117,10 @@ static int exec_mmap(struct mm_struct *mm)
setmax_mm_hiwater_rss(&tsk->signal->maxrss, old_mm);
mm_update_next_owner(old_mm);
mmput(old_mm);
- return 0;
+ } else {
+ exit_lazy_tlb(active_mm, tsk);
+ mmdrop(active_mm);
}
- mmdrop(active_mm);
return 0;
}

diff --git a/include/asm-generic/mmu_context.h b/include/asm-generic/mmu_context.h
index 86cea80a50df..3fc4c3879b79 100644
--- a/include/asm-generic/mmu_context.h
+++ b/include/asm-generic/mmu_context.h
@@ -24,6 +24,26 @@ static inline void enter_lazy_tlb(struct mm_struct *mm,
}
#endif

+/*
+ * exit_lazy_tlb - Called after switching away from a lazy TLB mode mm.
+ *
+ * mm: the lazy mm context that was switched away from
+ * tsk: the task that was switched to non-lazy mm
+ *
+ * tsk->mm will not be NULL.
+ *
+ * Note this is not symmetrical to enter_lazy_tlb, this is not
+ * called when tasks switch into the lazy mm, it's called after the
+ * lazy mm becomes non-lazy (either switched to a different mm or the
+ * owner of the mm returns).
+ */
+#ifndef exit_lazy_tlb
+static inline void exit_lazy_tlb(struct mm_struct *mm,
+ struct task_struct *tsk)
+{
+}
+#endif
+
/**
* init_new_context - Initialize context of a new mm_struct.
* @tsk: task struct for the mm
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 132f84a5fde3..e813d92f2eab 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -1253,6 +1253,7 @@ void kthread_use_mm(struct mm_struct *mm)

if (active_mm != mm)
mmdrop(active_mm);
+ exit_lazy_tlb(active_mm, tsk);

to_kthread(tsk)->oldfs = get_fs();
set_fs(USER_DS);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ca5db40392d4..debc917bc69b 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3439,6 +3439,8 @@ context_switch(struct rq *rq, struct task_struct *prev,
switch_mm_irqs_off(prev->active_mm, next->mm, next);

if (!prev->mm) { // from kernel
+ exit_lazy_tlb(prev->active_mm, next);
+
/* will mmdrop() in finish_task_switch(). */
rq->prev_mm = prev->active_mm;
prev->active_mm = NULL;
--
2.23.0