[PATCH] uevent: send events in correct order according to seqnum

[PATCH] uevent: send events in correct order according to seqnum

[Andrew Vagin]

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The queue handling in the udev daemon assumes that the events are
ordered.

Before this patch uevent_seqnum is incremented under sequence_lock,
than an event is send uner uevent_sock_mutex. I want to say that code
contained a window between incrementing seqnum and sending an event.

This patch locks uevent_sock_mutex before incrementing uevent_seqnum.

Signed-off-by: Andrew Vagin <avagin@openvz.org>
---
 lib/kobject_uevent.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)


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diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c
index e66e9b6..596c40d 100644
--- a/lib/kobject_uevent.c
+++ b/lib/kobject_uevent.c
@@ -243,6 +243,9 @@ int kobject_uevent_env(struct kobject *kobj, enum kobject_action action,
 	else if (action == KOBJ_REMOVE)
 		kobj->state_remove_uevent_sent = 1;
 
+#if defined(CONFIG_NET)
+	mutex_lock(&uevent_sock_mutex);
+#endif
 	/* we will send an event, so request a new sequence number */
 	spin_lock(&sequence_lock);
 	seq = ++uevent_seqnum;
@@ -253,7 +256,6 @@ int kobject_uevent_env(struct kobject *kobj, enum kobject_action action,
 
 #if defined(CONFIG_NET)
 	/* send netlink message */
-	mutex_lock(&uevent_sock_mutex);
 	list_for_each_entry(ue_sk, &uevent_sock_list, list) {
 		struct sock *uevent_sock = ue_sk->sk;
 		struct sk_buff *skb;

Re: [PATCH] uevent: send events in correct order according to seqnum

[Kay Sievers]

On Tue, Mar 6, 2012 at 21:06, Andrew Vagin <avagin@openvz.org> wrote:
>
> The queue handling in the udev daemon assumes that the events are
> ordered.
>
> Before this patch uevent_seqnum is incremented under sequence_lock,
> than an event is send uner uevent_sock_mutex. I want to say that code
> contained a window between incrementing seqnum and sending an event.
>
> This patch locks uevent_sock_mutex before incrementing uevent_seqnum.

I think we can remove the spin_lock(&sequence_lock); entirely now, right?

Also the section with:
  seq = ++uevent_seqnum;
can just be:
  add_uevent_var(env, "SEQNUM=%llu", (unsigned long long) ++uevent_seqnum);
right?

And the:
  mutex_lock(&uevent_sock_mutex);
can just move outside of the _NET ifdef and we always use the mutex
instead of the spinlock?

That could look much simpler than the current code, I think.

Thanks,
Kay

Re: [PATCH] uevent: send events in correct order according to seqnum

[avagin]

On 03/07/2012 01:03 AM, Kay Sievers wrote:
> On Tue, Mar 6, 2012 at 21:06, Andrew Vagin<avagin@openvz.org>  wrote:
>>
>> The queue handling in the udev daemon assumes that the events are
>> ordered.
>>
>> Before this patch uevent_seqnum is incremented under sequence_lock,
>> than an event is send uner uevent_sock_mutex. I want to say that code
>> contained a window between incrementing seqnum and sending an event.
>>
>> This patch locks uevent_sock_mutex before incrementing uevent_seqnum.
>
> I think we can remove the spin_lock(&sequence_lock); entirely now, right?

I thought about that too. sequence_lock is used when CONFIG_NET isn't 
defined. I've looked on this code one more time and we may leave only 
uevent_sock_mutex and use it even when CONFIG_NET isn't defined.
Thanks for the comment.

Greg, do you have other objections about this patch?

>
> Also the section with:
>    seq = ++uevent_seqnum;
> can just be:
>    add_uevent_var(env, "SEQNUM=%llu", (unsigned long long) ++uevent_seqnum);
> right?
>
> And the:
>    mutex_lock(&uevent_sock_mutex);
> can just move outside of the _NET ifdef and we always use the mutex
> instead of the spinlock?
>
> That could look much simpler than the current code, I think.
>
> Thanks,
> Kay

Re: [PATCH] uevent: send events in correct order according to seqnum

[Greg Kroah-Hartman]

On Wed, Mar 07, 2012 at 01:14:04AM +0400, avagin@gmail.com wrote:
> On 03/07/2012 01:03 AM, Kay Sievers wrote:
> >On Tue, Mar 6, 2012 at 21:06, Andrew Vagin<avagin@openvz.org>  wrote:
> >>
> >>The queue handling in the udev daemon assumes that the events are
> >>ordered.
> >>
> >>Before this patch uevent_seqnum is incremented under sequence_lock,
> >>than an event is send uner uevent_sock_mutex. I want to say that code
> >>contained a window between incrementing seqnum and sending an event.
> >>
> >>This patch locks uevent_sock_mutex before incrementing uevent_seqnum.
> >
> >I think we can remove the spin_lock(&sequence_lock); entirely now, right?
> 
> I thought about that too. sequence_lock is used when CONFIG_NET
> isn't defined. I've looked on this code one more time and we may
> leave only uevent_sock_mutex and use it even when CONFIG_NET isn't
> defined.
> Thanks for the comment.
> 
> Greg, do you have other objections about this patch?

Let's see the one based on Kay's comments first please.

thanks,

greg k-h