* [B.A.T.M.A.N.] [PATCH] batman-adv: Always synchronize rcu's on module shutdown
@ 2010-09-05 23:29 Linus Lüssing
2010-09-06 7:30 ` Sven Eckelmann
0 siblings, 1 reply; 7+ messages in thread
From: Linus Lüssing @ 2010-09-05 23:29 UTC (permalink / raw)
To: b.a.t.m.a.n
During the module shutdown procedure in batman_exit(), a rcu callback is
being scheduled (batman_exit -> hardif_remove_interfaces ->
hardif_remove_interfae -> call_rcu). However, when the kernel unloads
the module, the rcu callback might not have been executed yet, resulting
in a "unable to handle kernel paging request" in __rcu_process_callback
afterwards, causing the kernel to freeze.
Therefore, we should always flush all rcu callback functions scheduled
during the shutdown procedure.
Signed-off-by: Linus Lüssing <linus.luessing@web.de>
---
main.c | 5 ++---
1 files changed, 2 insertions(+), 3 deletions(-)
diff --git a/main.c b/main.c
index 209a46b..e8acb46 100644
--- a/main.c
+++ b/main.c
@@ -73,6 +73,8 @@ static void __exit batman_exit(void)
flush_workqueue(bat_event_workqueue);
destroy_workqueue(bat_event_workqueue);
bat_event_workqueue = NULL;
+
+ synchronize_net();
}
int mesh_init(struct net_device *soft_iface)
@@ -135,9 +137,6 @@ void mesh_free(struct net_device *soft_iface)
hna_local_free(bat_priv);
hna_global_free(bat_priv);
- synchronize_net();
-
- synchronize_rcu();
atomic_set(&bat_priv->mesh_state, MESH_INACTIVE);
}
--
1.7.1
^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [B.A.T.M.A.N.] [PATCH] batman-adv: Always synchronize rcu's on module shutdown
2010-09-05 23:29 [B.A.T.M.A.N.] [PATCH] batman-adv: Always synchronize rcu's on module shutdown Linus Lüssing
@ 2010-09-06 7:30 ` Sven Eckelmann
2010-09-06 10:09 ` Linus Lüssing
0 siblings, 1 reply; 7+ messages in thread
From: Sven Eckelmann @ 2010-09-06 7:30 UTC (permalink / raw)
To: The list for a Better Approach To Mobile Ad-hoc Networking
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On Mon, Sep 06, 2010 at 01:29:53AM +0200, Linus Lüssing wrote:
> During the module shutdown procedure in batman_exit(), a rcu callback is
> being scheduled (batman_exit -> hardif_remove_interfaces ->
> hardif_remove_interfae -> call_rcu). However, when the kernel unloads
> the module, the rcu callback might not have been executed yet, resulting
> in a "unable to handle kernel paging request" in __rcu_process_callback
> afterwards, causing the kernel to freeze.
> Therefore, we should always flush all rcu callback functions scheduled
> during the shutdown procedure.
I am really irritated by your patch. I would have expected that you add a
synchronyze_rcu in batman_exit and that was it. Instead I see a synchronize_net
added and a synchronize_net/-_rcu removed from mesh_free. This doesn't seem to
match at all. Could you please explain further why it is implemented that way?
thanks,
Sven
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^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [B.A.T.M.A.N.] [PATCH] batman-adv: Always synchronize rcu's on module shutdown
2010-09-06 7:30 ` Sven Eckelmann
@ 2010-09-06 10:09 ` Linus Lüssing
2010-09-06 12:07 ` Sven Eckelmann
0 siblings, 1 reply; 7+ messages in thread
From: Linus Lüssing @ 2010-09-06 10:09 UTC (permalink / raw)
To: The list for a Better Approach To Mobile Ad-hoc Networking
Hi Sven,
synchronize_net already contains a synchronize_rcu at its end, so
the synchronize_rcu in the batman code there has always been
redundant.
I've removed the synchronize_rcu instead of the synchronize_net to
be on the safe side. I guess usually no more packets should arrive
anyway as the batman packet type is not registered anymore. But I
wasn't sure if the might_sleep() of synchronize_net() might be
needed for something, so I didn't dare to remove synchronize_net.
If someone says it'd be ok to remove synchronize_net() instead,
I could make a new patch, no problem.
Cheers, Linus
On Mon, Sep 06, 2010 at 09:30:46AM +0200, Sven Eckelmann wrote:
> On Mon, Sep 06, 2010 at 01:29:53AM +0200, Linus Lüssing wrote:
> > During the module shutdown procedure in batman_exit(), a rcu callback is
> > being scheduled (batman_exit -> hardif_remove_interfaces ->
> > hardif_remove_interfae -> call_rcu). However, when the kernel unloads
> > the module, the rcu callback might not have been executed yet, resulting
> > in a "unable to handle kernel paging request" in __rcu_process_callback
> > afterwards, causing the kernel to freeze.
> > Therefore, we should always flush all rcu callback functions scheduled
> > during the shutdown procedure.
>
> I am really irritated by your patch. I would have expected that you add a
> synchronyze_rcu in batman_exit and that was it. Instead I see a synchronize_net
> added and a synchronize_net/-_rcu removed from mesh_free. This doesn't seem to
> match at all. Could you please explain further why it is implemented that way?
>
> thanks,
> Sven
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [B.A.T.M.A.N.] [PATCH] batman-adv: Always synchronize rcu's on module shutdown
2010-09-06 10:09 ` Linus Lüssing
@ 2010-09-06 12:07 ` Sven Eckelmann
2010-09-06 12:37 ` Linus Lüssing
0 siblings, 1 reply; 7+ messages in thread
From: Sven Eckelmann @ 2010-09-06 12:07 UTC (permalink / raw)
To: b.a.t.m.a.n
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Linus Lüssing wrote:
> Hi Sven,
>
> synchronize_net already contains a synchronize_rcu at its end, so
> the synchronize_rcu in the batman code there has always been
> redundant.
>
> I've removed the synchronize_rcu instead of the synchronize_net to
> be on the safe side. I guess usually no more packets should arrive
> anyway as the batman packet type is not registered anymore. But I
> wasn't sure if the might_sleep() of synchronize_net() might be
> needed for something, so I didn't dare to remove synchronize_net.
>
> If someone says it'd be ok to remove synchronize_net() instead,
> I could make a new patch, no problem.
Ok, it would have been nice to state such things in the commit message
(otherwise the stable@kernel.org will drop such a patch quite easily). Marek
and I have ausgekaspert why it only happens in 1765 and also in 1766. So it
will not be a patch for stable.
And the might_sleep is only for debugging purposes. But yes, it makes sense to
use synchronize_net here (for example due to the usage of dev_remove_pack
before).
That means that technically the patch seems to be ok, but didn't liked the
explanation with the problem that we might have to justify it to the
stable@kernel.org guys that way.
So I would ack the patch with a minor change in the commit message. So instead
of
> During the module shutdown procedure in batman_exit(), a rcu callback is
> being scheduled (batman_exit -> hardif_remove_interfaces ->
> hardif_remove_interfae -> call_rcu). However, when the kernel unloads
> the module, the rcu callback might not have been executed yet, resulting
> in a "unable to handle kernel paging request" in __rcu_process_callback
> afterwards, causing the kernel to freeze.
> Therefore, we should always flush all rcu callback functions scheduled
> during the shutdown procedure.
something like
> During the module shutdown procedure in batman_exit(), a rcu callback is
> being scheduled (batman_exit -> hardif_remove_interfaces ->
> hardif_remove_interfae -> call_rcu). However, when the kernel unloads
> the module, the rcu callback might not have been executed yet, resulting
> in a "unable to handle kernel paging request" in __rcu_process_callback
> afterwards, causing the kernel to freeze.
> The synchronize_net and synchronize_rcu in mesh_free are currently
> called before the call_rcu in hardif_remove_interface and have no real
> effect on it.
> Therefore, we should always flush all rcu callback functions scheduled
> during the shutdown procedure using synchronize_net. The call to
> synchronize_rcu can be omitted because synchronize_net already calls it.
thanks,
Sven
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^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [B.A.T.M.A.N.] [PATCH] batman-adv: Always synchronize rcu's on module shutdown
2010-09-06 12:07 ` Sven Eckelmann
@ 2010-09-06 12:37 ` Linus Lüssing
2010-09-06 12:45 ` [B.A.T.M.A.N.] [PATCHv2] " Sven Eckelmann
0 siblings, 1 reply; 7+ messages in thread
From: Linus Lüssing @ 2010-09-06 12:37 UTC (permalink / raw)
To: Sven Eckelmann; +Cc: b.a.t.m.a.n
> So I would ack the patch with a minor change in the commit message. So instead
> of
>
> > During the module shutdown procedure in batman_exit(), a rcu callback is
> > being scheduled (batman_exit -> hardif_remove_interfaces ->
> > hardif_remove_interfae -> call_rcu). However, when the kernel unloads
> > the module, the rcu callback might not have been executed yet, resulting
> > in a "unable to handle kernel paging request" in __rcu_process_callback
> > afterwards, causing the kernel to freeze.
> > Therefore, we should always flush all rcu callback functions scheduled
> > during the shutdown procedure.
>
> something like
>
> > During the module shutdown procedure in batman_exit(), a rcu callback is
> > being scheduled (batman_exit -> hardif_remove_interfaces ->
> > hardif_remove_interfae -> call_rcu). However, when the kernel unloads
> > the module, the rcu callback might not have been executed yet, resulting
> > in a "unable to handle kernel paging request" in __rcu_process_callback
> > afterwards, causing the kernel to freeze.
>
> > The synchronize_net and synchronize_rcu in mesh_free are currently
> > called before the call_rcu in hardif_remove_interface and have no real
> > effect on it.
>
> > Therefore, we should always flush all rcu callback functions scheduled
> > during the shutdown procedure using synchronize_net. The call to
> > synchronize_rcu can be omitted because synchronize_net already calls it.
Yep, sounds good :). Thanks for reviewing and the info about
synchronize_net.
Cheers, Linus
>
> thanks,
> Sven
^ permalink raw reply [flat|nested] 7+ messages in thread
* [B.A.T.M.A.N.] [PATCHv2] batman-adv: Always synchronize rcu's on module shutdown
2010-09-06 12:37 ` Linus Lüssing
@ 2010-09-06 12:45 ` Sven Eckelmann
2010-09-06 14:09 ` Marek Lindner
0 siblings, 1 reply; 7+ messages in thread
From: Sven Eckelmann @ 2010-09-06 12:45 UTC (permalink / raw)
To: b.a.t.m.a.n
From: Linus Lüssing <linus.luessing@web.de>
During the module shutdown procedure in batman_exit(), a rcu callback is
being scheduled (batman_exit -> hardif_remove_interfaces ->
hardif_remove_interfae -> call_rcu). However, when the kernel unloads
the module, the rcu callback might not have been executed yet, resulting
in a "unable to handle kernel paging request" in __rcu_process_callback
afterwards, causing the kernel to freeze.
The synchronize_net and synchronize_rcu in mesh_free are currently
called before the call_rcu in hardif_remove_interface and have no real
effect on it.
Therefore, we should always flush all rcu callback functions scheduled
during the shutdown procedure using synchronize_net. The call to
synchronize_rcu can be omitted because synchronize_net already calls it.
Signed-off-by: Linus Lüssing <linus.luessing@web.de>
Acked-by: Sven Eckelmann <sven.eckelmann@gmx.de>
---
batman-adv/main.c | 5 ++---
1 files changed, 2 insertions(+), 3 deletions(-)
diff --git a/batman-adv/main.c b/batman-adv/main.c
index 209a46b..e8acb46 100644
--- a/batman-adv/main.c
+++ b/batman-adv/main.c
@@ -73,6 +73,8 @@ static void __exit batman_exit(void)
flush_workqueue(bat_event_workqueue);
destroy_workqueue(bat_event_workqueue);
bat_event_workqueue = NULL;
+
+ synchronize_net();
}
int mesh_init(struct net_device *soft_iface)
@@ -135,9 +137,6 @@ void mesh_free(struct net_device *soft_iface)
hna_local_free(bat_priv);
hna_global_free(bat_priv);
- synchronize_net();
-
- synchronize_rcu();
atomic_set(&bat_priv->mesh_state, MESH_INACTIVE);
}
--
1.7.1
^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [B.A.T.M.A.N.] [PATCHv2] batman-adv: Always synchronize rcu's on module shutdown
2010-09-06 12:45 ` [B.A.T.M.A.N.] [PATCHv2] " Sven Eckelmann
@ 2010-09-06 14:09 ` Marek Lindner
0 siblings, 0 replies; 7+ messages in thread
From: Marek Lindner @ 2010-09-06 14:09 UTC (permalink / raw)
To: The list for a Better Approach To Mobile Ad-hoc Networking
On Monday 06 September 2010 14:45:24 Sven Eckelmann wrote:
> Therefore, we should always flush all rcu callback functions scheduled
> during the shutdown procedure using synchronize_net. The call to
> synchronize_rcu can be omitted because synchronize_net already calls it.
Applied in revision 1788.
Thanks,
Marek
^ permalink raw reply [flat|nested] 7+ messages in thread
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2010-09-05 23:29 [B.A.T.M.A.N.] [PATCH] batman-adv: Always synchronize rcu's on module shutdown Linus Lüssing
2010-09-06 7:30 ` Sven Eckelmann
2010-09-06 10:09 ` Linus Lüssing
2010-09-06 12:07 ` Sven Eckelmann
2010-09-06 12:37 ` Linus Lüssing
2010-09-06 12:45 ` [B.A.T.M.A.N.] [PATCHv2] " Sven Eckelmann
2010-09-06 14:09 ` Marek Lindner
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