linux-kernel - [PATCH 1/5] vfork: don't freezer_count() for in-kernel users of CLONE

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Message-Id: <1360885096-21207-1-git-send-email-msb@chromium.org>
Date:	Thu, 14 Feb 2013 15:38:12 -0800
From:	Mandeep Singh Baines <msb@...omium.org>
To:	linux-kernel@...r.kernel.org
Cc:	Mandeep Singh Baines <msb@...omium.org>,
	Oleg Nesterov <oleg@...hat.com>, Tejun Heo <tj@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Ingo Molnar <mingo@...hat.com>
Subject: [PATCH 1/5] vfork: don't freezer_count() for in-kernel users of CLONE_VFORK

We don't need to call freezer_do_not_count() for in-kernel users
of CLONE_VFORK since exec will get called in bounded time.

We don't want to call freezer_count() for in-kernel users because
they may be holding locks. freezer_count() calls try_to_freeze().
We don't want to freeze an in-kernel user because it may be
holding locks.

In a follow-up patch, I call debug_check_no_locks_held() from
try_to_freeze(). After applying this patch, I get no lockdep
warnings with that patch.

Signed-off-by: Mandeep Singh Baines <msb@...omium.org>
CC: Oleg Nesterov <oleg@...hat.com>
CC: Tejun Heo <tj@...nel.org>
CC: Andrew Morton <akpm@...ux-foundation.org>
CC: Rafael J. Wysocki <rjw@...k.pl>
CC: Ingo Molnar <mingo@...hat.com>
---
 kernel/fork.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index c535f33..a7cd973 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -722,9 +722,11 @@ static int wait_for_vfork_done(struct task_struct *child,
 {
 	int killed;
 
-	freezer_do_not_count();
+	if (current->mm)
+		freezer_do_not_count();
 	killed = wait_for_completion_killable(vfork);
-	freezer_count();
+	if (current->mm)
+		freezer_count();
 
 	if (killed) {
 		task_lock(child);
-- 
1.8.1

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