linux-kernel - [PATCH 1/1] kthread: disable preemption during complete()

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 24 Jul 2012 17:05:32 -0700
From:	Peter Boonstoppel <pboonstoppel@...dia.com>
To:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Tejun Heo <tj@...nel.org>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Henrique de Moraes Holschuh <ibm-acpi@....eng.br>,
	Andy Walls <awalls@...metrocast.net>
CC:	Diwakar Tundlam <dtundlam@...dia.com>
Subject: [PATCH 1/1] kthread: disable preemption during complete()

After a kthread is created it signals the requester using complete()
and enters TASK_UNINTERRUPTIBLE. However, since complete() wakes up
the requesting thread this can cause a preemption. The preemption will
not remove the task from the runqueue (for that schedule() has to be
invoked directly).

This is a problem if directly after kthread creation you try to do a
kthread_bind(), which will block in HZ steps until the thread is off
the runqueue.

This patch disables preemption during complete(), since we call
schedule() directly afterwards, so it will correctly enter
TASK_UNINTERRUPTIBLE. This speeds up kthread creation/binding during
cpu hotplug significantly.

Change-Id: I856ddd4e01ebdb198ba90f343b4a0c5933fd2b23
Signed-off-by: Peter Boonstoppel <pboonstoppel@...dia.com>
---
 kernel/kthread.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/kernel/kthread.c b/kernel/kthread.c
index b579af5..f681b14 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -16,6 +16,8 @@
 #include <linux/mutex.h>
 #include <linux/slab.h>
 #include <linux/freezer.h>
+#include <linux/preempt.h>
+#include <linux/thread_info.h>
 #include <trace/events/sched.h>
 
 static DEFINE_SPINLOCK(kthread_create_lock);
@@ -113,7 +115,10 @@ static int kthread(void *_create)
 	/* OK, tell user we're spawned, wait for stop or wakeup */
 	__set_current_state(TASK_UNINTERRUPTIBLE);
 	create->result = current;
+	preempt_disable();
 	complete(&create->done);
+	clear_need_resched();
+	preempt_enable_no_resched();
 	schedule();
 
 	ret = -EINTR;
-- 
1.7.0.4
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/