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-rw-r--r--kernel/kthread.c21
1 files changed, 21 insertions, 0 deletions
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 933a625621b8..e6aa66551241 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -1249,6 +1249,7 @@ void kthread_use_mm(struct mm_struct *mm)
tsk->active_mm = mm;
}
tsk->mm = mm;
+ membarrier_update_current_mm(mm);
switch_mm_irqs_off(active_mm, mm, tsk);
local_irq_enable();
task_unlock(tsk);
@@ -1256,8 +1257,19 @@ void kthread_use_mm(struct mm_struct *mm)
finish_arch_post_lock_switch();
#endif
+ /*
+ * When a kthread starts operating on an address space, the loop
+ * in membarrier_{private,global}_expedited() may not observe
+ * that tsk->mm, and not issue an IPI. Membarrier requires a
+ * 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().
+ */
if (active_mm != mm)
mmdrop(active_mm);
+ else
+ smp_mb();
to_kthread(tsk)->oldfs = force_uaccess_begin();
}
@@ -1277,9 +1289,18 @@ void kthread_unuse_mm(struct mm_struct *mm)
force_uaccess_end(to_kthread(tsk)->oldfs);
task_lock(tsk);
+ /*
+ * When a kthread stops operating on an address space, the loop
+ * in membarrier_{private,global}_expedited() may not observe
+ * that tsk->mm, and not issue an IPI. Membarrier requires a
+ * memory barrier after accessing user-space memory, before
+ * clearing tsk->mm.
+ */
+ smp_mb__after_spinlock();
sync_mm_rss(mm);
local_irq_disable();
tsk->mm = NULL;
+ membarrier_update_current_mm(NULL);
/* active_mm is still 'mm' */
enter_lazy_tlb(mm, tsk);
local_irq_enable();