2015-07-08 19:43:48

by Oleg Nesterov

Subject: [PATCH 0/2] net: pktgen: fix race between pktgen_thread_worker() and kthread_stop()

Hello,

I am not familiar with this code and I have no idea how to test
these changes, so 2/2 comes as a separate change. 1/2 looks like
the obvious bugfix, and probably candidate for -stable.

Oleg.

net/core/pktgen.c | 9 ++-------
1 files changed, 2 insertions(+), 7 deletions(-)

2015-07-08 19:44:06

by Oleg Nesterov

Subject: [PATCH 1/2] net: pktgen: fix race between pktgen_thread_worker() and kthread_stop()

pktgen_thread_worker() is obviously racy, kthread_stop() can come
between the kthread_should_stop() check and set_current_state().

Signed-off-by: Oleg Nesterov <[email protected]>
Reported-by: Jan Stancek <[email protected]>
Reported-by: Marcelo Leitner <[email protected]>
---
net/core/pktgen.c | 4 +++-
1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/net/core/pktgen.c b/net/core/pktgen.c
index 508155b..043ea18 100644
--- a/net/core/pktgen.c
+++ b/net/core/pktgen.c
@@ -3490,8 +3490,10 @@ static int pktgen_thread_worker(void *arg)
pktgen_rem_thread(t);

/* Wait for kthread_stop */
- while (!kthread_should_stop()) {
+ for (;;) {
set_current_state(TASK_INTERRUPTIBLE);
+ if (kthread_should_stop())
+ break;
schedule();
}
__set_current_state(TASK_RUNNING);
--
1.5.5.1

2015-07-08 19:43:54

by Oleg Nesterov

Subject: [PATCH 2/2] net: pktgen: kill the "Wait for kthread_stop" code in pktgen_thread_worker()

pktgen_thread_worker() doesn't need to wait for kthread_stop(), it
can simply exit. Just pktgen_create_thread() and pg_net_exit() should
do get_task_struct()/put_task_struct(). kthread_stop(dead_thread) is
fine.

Signed-off-by: Oleg Nesterov <[email protected]>
---
net/core/pktgen.c | 11 ++---------
1 files changed, 2 insertions(+), 9 deletions(-)

diff --git a/net/core/pktgen.c b/net/core/pktgen.c
index 043ea18..8e0181a 100644
--- a/net/core/pktgen.c
+++ b/net/core/pktgen.c
@@ -3489,15 +3489,6 @@ static int pktgen_thread_worker(void *arg)
pr_debug("%s removing thread\n", t->tsk->comm);
pktgen_rem_thread(t);

- /* Wait for kthread_stop */
- for (;;) {
- set_current_state(TASK_INTERRUPTIBLE);
- if (kthread_should_stop())
- break;
- schedule();
- }
- __set_current_state(TASK_RUNNING);
-
return 0;
}

@@ -3689,6 +3680,7 @@ static int __net_init pktgen_create_thread(int cpu, struct pktgen_net *pn)
}

t->net = pn;
+ get_task_struct(p);
wake_up_process(p);
wait_for_completion(&t->start_done);

@@ -3811,6 +3803,7 @@ static void __net_exit pg_net_exit(struct net *net)
t = list_entry(q, struct pktgen_thread, th_list);
list_del(&t->th_list);
kthread_stop(t->tsk);
+ put_task_struct(t->tsk);
kfree(t);
}

--
1.5.5.1

2015-07-09 22:06:16

by David Miller

Subject: Re: [PATCH 0/2] net: pktgen: fix race between pktgen_thread_worker() and kthread_stop()

From: Oleg Nesterov <[email protected]>
Date: Wed, 8 Jul 2015 21:41:54 +0200

> I am not familiar with this code and I have no idea how to test
> these changes, so 2/2 comes as a separate change. 1/2 looks like
> the obvious bugfix, and probably candidate for -stable.

These look fine to me, applied and patch #1 queued up for -stable.

Thanks.

2015-07-10 11:32:59

by Marcelo Ricardo Leitner

Subject: Re: [PATCH 0/2] net: pktgen: fix race between pktgen_thread_worker() and kthread_stop()

On Wed, Jul 08, 2015 at 09:41:54PM +0200, Oleg Nesterov wrote:
> Hello,
>
> I am not familiar with this code and I have no idea how to test
> these changes, so 2/2 comes as a separate change. 1/2 looks like
> the obvious bugfix, and probably candidate for -stable.
>
> Oleg.
>
> net/core/pktgen.c | 9 ++-------
> 1 files changed, 2 insertions(+), 7 deletions(-)
>

Both patches tested here, works for me.

Thanks,
Marcelo