[PATCH] fork: clarify copy_mm() comment for kernel thread

[Minu Jin <s9430939@naver.com>]

The existing comment is misleading:

    1. "steal a active VM" suggests this code performs the active_mm
       borrowing, but the actual borrowing happens in context_switch()
       where 'next->active_mm = prev->active_mm' is assigned.
       This code simply returns 0 to skip mm copying for kernel threads.

    2. "active VM" is outdated terminology, the kernel uses "active_mm".

Update the comment to accurately describe what this code does.

Signed-off-by: Minu Jin <s9430939@naver.com>
---
 kernel/fork.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index b1f3915d5f8e..4bfd606004db 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1566,9 +1566,10 @@ static int copy_mm(u64 clone_flags, struct task_struct *tsk)
 	tsk->active_mm = NULL;
 
 	/*
-	 * Are we cloning a kernel thread?
+	 * Kernel threads have no 'mm' of their own as they borrow the
+	 * 'active_mm' from the previous process at context_switch().
 	 *
-	 * We need to steal a active VM for that..
+	 * Return 0 directly to skip the copy_mm process.
 	 */
 	oldmm = current->mm;
 	if (!oldmm)
-- 
2.43.0