linux-kernel - [PATCH 1/4] kernel/exit: Compute current directly

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Date:   Tue,  3 Jan 2017 13:43:11 -0800
From:   Davidlohr Bueso <dave@...olabs.net>
To:     mingo@...nel.org, akpm@...ux-foundation.org
Cc:     peterz@...radead.org, torvalds@...ux-foundation.org,
        mark.rutland@....com, dave@...olabs.net,
        linux-kernel@...r.kernel.org, Davidlohr Bueso <dbueso@...e.de>
Subject: [PATCH 1/4] kernel/exit: Compute current directly

This patch effectively replaces the tsk pointer dereference
(which is obviously == current), to directly use get_current()
macro. In this case, do_exit() always passes current to exit_mm(),
hence we can simply get rid of the arg. This is also a performance
win on some archs such as x86-64 and ppc64 -- arm64 is no longer
an issue:

    https://lkml.org/lkml/2016/12/30/230

Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
---
XXX: do_exit() could further be cleaned up and we'd endup getting
rid of tsk for a lot of the exit_*() calls.

 kernel/exit.c | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index 8f14b866f9f6..2385d434a46e 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -468,12 +468,12 @@ void mm_update_next_owner(struct mm_struct *mm)
  * Turn us into a lazy TLB process if we
  * aren't already..
  */
-static void exit_mm(struct task_struct *tsk)
+static void exit_mm(void)
 {
-	struct mm_struct *mm = tsk->mm;
+	struct mm_struct *mm = current->mm;
 	struct core_state *core_state;
 
-	mm_release(tsk, mm);
+	mm_release(current, mm);
 	if (!mm)
 		return;
 	sync_mm_rss(mm);
@@ -491,7 +491,7 @@ static void exit_mm(struct task_struct *tsk)
 
 		up_read(&mm->mmap_sem);
 
-		self.task = tsk;
+		self.task = current;
 		self.next = xchg(&core_state->dumper.next, &self);
 		/*
 		 * Implies mb(), the result of xchg() must be visible
@@ -501,22 +501,22 @@ static void exit_mm(struct task_struct *tsk)
 			complete(&core_state->startup);
 
 		for (;;) {
-			set_task_state(tsk, TASK_UNINTERRUPTIBLE);
+			set_task_state(current, TASK_UNINTERRUPTIBLE);
 			if (!self.task) /* see coredump_finish() */
 				break;
 			freezable_schedule();
 		}
-		__set_task_state(tsk, TASK_RUNNING);
+		__set_task_state(current, TASK_RUNNING);
 		down_read(&mm->mmap_sem);
 	}
 	atomic_inc(&mm->mm_count);
-	BUG_ON(mm != tsk->active_mm);
+	BUG_ON(mm != current->active_mm);
 	/* more a memory barrier than a real lock */
-	task_lock(tsk);
-	tsk->mm = NULL;
+	task_lock(current);
+	current->mm = NULL;
 	up_read(&mm->mmap_sem);
 	enter_lazy_tlb(mm, current);
-	task_unlock(tsk);
+	task_unlock(current);
 	mm_update_next_owner(mm);
 	mmput(mm);
 	if (test_thread_flag(TIF_MEMDIE))
@@ -823,7 +823,7 @@ void __noreturn do_exit(long code)
 	tsk->exit_code = code;
 	taskstats_exit(tsk, group_dead);
 
-	exit_mm(tsk);
+	exit_mm();
 
 	if (group_dead)
 		acct_process();
-- 
2.6.6