Re: [PATCH] netdev: Fix sleeping inside wait event

Re: [PATCH] netdev: Fix sleeping inside wait event

[Cong Wang]

(Adding netdev@...)

On Wed, Oct 29, 2014 at 9:16 AM, Peter Zijlstra <peterz@infradead.org> wrote:
>
> Dave, this relies on bits currently in tip/sched/core, if you're ok I'll
> merge it through that tree.
>
> ---
> Subject: netdev: Fix sleeping inside wait event
> From: Peter Zijlstra <peterz@infradead.org>
> Date: Wed Oct 29 17:04:56 CET 2014
>
> rtnl_lock_unregistering() takes rtnl_lock() -- a mutex -- inside a
> wait loop. The wait loop relies on current->state to function, but so
> does mutex_lock(), nesting them makes for the inner to destroy the
> outer state.
>

While you are on it, please fix rtnl_lock_unregistering_all() too?

Thanks!

> Fix this using the new wait_woken() bits.
>
> Cc: Oleg Nesterov <oleg@redhat.com>
> Cc: Eric Biederman <ebiederm@xmission.com>
> Cc: David Miller <davem@davemloft.net>
> Reported-by: Fengguang Wu <fengguang.wu@intel.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
>  net/core/dev.c |   10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
>
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -7196,11 +7196,10 @@ static void __net_exit rtnl_lock_unregis
>          */
>         struct net *net;
>         bool unregistering;
> -       DEFINE_WAIT(wait);
> +       DEFINE_WAIT_FUNC(wait, woken_wake_function);
>
> +       add_wait_queue(&netdev_unregistering_wq, &wait);
>         for (;;) {
> -               prepare_to_wait(&netdev_unregistering_wq, &wait,
> -                               TASK_UNINTERRUPTIBLE);
>                 unregistering = false;
>                 rtnl_lock();
>                 list_for_each_entry(net, net_list, exit_list) {
> @@ -7212,9 +7211,10 @@ static void __net_exit rtnl_lock_unregis
>                 if (!unregistering)
>                         break;
>                 __rtnl_unlock();
> -               schedule();
> +
> +               wait_woken(&wait, TASK_UNINTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
>         }
> -       finish_wait(&netdev_unregistering_wq, &wait);
> +       remove_wait_queue(&netdev_unregistering_wq, &wait);
>  }
>
>  static void __net_exit default_device_exit_batch(struct list_head *net_list)
> --
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Re: [PATCH] netdev: Fix sleeping inside wait event

[Peter Zijlstra]

On Wed, Oct 29, 2014 at 09:29:55AM -0700, Cong Wang wrote:
> (Adding netdev@...)
> 
> On Wed, Oct 29, 2014 at 9:16 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > Dave, this relies on bits currently in tip/sched/core, if you're ok I'll
> > merge it through that tree.
> >
> > ---
> > Subject: netdev: Fix sleeping inside wait event
> > From: Peter Zijlstra <peterz@infradead.org>
> > Date: Wed Oct 29 17:04:56 CET 2014
> >
> > rtnl_lock_unregistering() takes rtnl_lock() -- a mutex -- inside a
> > wait loop. The wait loop relies on current->state to function, but so
> > does mutex_lock(), nesting them makes for the inner to destroy the
> > outer state.
> >
> 
> While you are on it, please fix rtnl_lock_unregistering_all() too?

Ah, that's hidden someplace else, sure I can do that. Thanks for
pointing it out.

Re: [PATCH] netdev: Fix sleeping inside wait event

[Peter Zijlstra]

On Wed, Oct 29, 2014 at 06:13:45PM +0100, Peter Zijlstra wrote:
> On Wed, Oct 29, 2014 at 09:29:55AM -0700, Cong Wang wrote:
> > While you are on it, please fix rtnl_lock_unregistering_all() too?
> 
> Ah, that's hidden someplace else, sure I can do that. Thanks for
> pointing it out.

Here goes..

---
Subject: netdev: Fix sleeping inside wait event
From: Peter Zijlstra <peterz@infradead.org>
Date: Wed Oct 29 17:04:56 CET 2014

rtnl_lock_unregistering*() take rtnl_lock() -- a mutex -- inside a
wait loop. The wait loop relies on current->state to function, but so
does mutex_lock(), nesting them makes for the inner to destroy the
outer state.

Fix this using the new wait_woken() bits.

Cc: David Miller <davem@davemloft.net>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 net/core/dev.c       |   10 +++++-----
 net/core/rtnetlink.c |   10 +++++-----
 2 files changed, 10 insertions(+), 10 deletions(-)

--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -7196,11 +7196,10 @@ static void __net_exit rtnl_lock_unregis
 	 */
 	struct net *net;
 	bool unregistering;
-	DEFINE_WAIT(wait);
+	DEFINE_WAIT_FUNC(wait, woken_wake_function);
 
+	add_wait_queue(&netdev_unregistering_wq, &wait);
 	for (;;) {
-		prepare_to_wait(&netdev_unregistering_wq, &wait,
-				TASK_UNINTERRUPTIBLE);
 		unregistering = false;
 		rtnl_lock();
 		list_for_each_entry(net, net_list, exit_list) {
@@ -7212,9 +7211,10 @@ static void __net_exit rtnl_lock_unregis
 		if (!unregistering)
 			break;
 		__rtnl_unlock();
-		schedule();
+
+		wait_woken(&wait, TASK_UNINTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
 	}
-	finish_wait(&netdev_unregistering_wq, &wait);
+	remove_wait_queue(&netdev_unregistering_wq, &wait);
 }
 
 static void __net_exit default_device_exit_batch(struct list_head *net_list)
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -365,11 +365,10 @@ static void rtnl_lock_unregistering_all(
 {
 	struct net *net;
 	bool unregistering;
-	DEFINE_WAIT(wait);
+	DEFINE_WAIT_FUNC(wait, woken_wake_function);
 
+	add_wait_queue(&netdev_unregistering_wq, &wait);
 	for (;;) {
-		prepare_to_wait(&netdev_unregistering_wq, &wait,
-				TASK_UNINTERRUPTIBLE);
 		unregistering = false;
 		rtnl_lock();
 		for_each_net(net) {
@@ -381,9 +380,10 @@ static void rtnl_lock_unregistering_all(
 		if (!unregistering)
 			break;
 		__rtnl_unlock();
-		schedule();
+
+		wait_woken(&wait, TASK_UNINTERRUPTIBLE, MAX_SCHEDULE_TIMEOUT);
 	}
-	finish_wait(&netdev_unregistering_wq, &wait);
+	remove_wait_queue(&netdev_unregistering_wq, &wait);
 }
 
 /**

Re: [PATCH] netdev: Fix sleeping inside wait event

[David Miller]

From: Peter Zijlstra <peterz@infradead.org>
Date: Wed, 29 Oct 2014 18:31:10 +0100

> On Wed, Oct 29, 2014 at 06:13:45PM +0100, Peter Zijlstra wrote:
>> On Wed, Oct 29, 2014 at 09:29:55AM -0700, Cong Wang wrote:
>> > While you are on it, please fix rtnl_lock_unregistering_all() too?
>> 
>> Ah, that's hidden someplace else, sure I can do that. Thanks for
>> pointing it out.
> 
> Here goes..

For this as well:

Acked-by: David S. Miller <davem@davemloft.net>