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SubjectRe: [Linux 4.2-rc8+...v4.3-rc2] REGRESSION: ppp: circular locking dependency detected: [pppd] ppp_dev_uninit() | rtnl_lock()
From
On Wed, Sep 23, 2015 at 12:38 PM, Guillaume Nault <g.nault@alphalink.fr> wrote:
> On Wed, Sep 23, 2015 at 08:06:16AM +0200, Sedat Dilek wrote:
>> Without reverting the below culprit ppp patch...
>>
>> commit/?id=8cb775bc0a34dc596837e7da03fd22c747be618b
>> ("ppp: fix device unregistration upon netns deletion")
>>
>> ...I have an unstable Internet connection via Network-Manager/ModemManager.
>>
>> First I saw this with Linux v4.2.
>>
>
> Thanks for reporting the issue. Can you test this patch ?
>
> ---
> diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c
> index 0481daf..ed00446 100644
> --- a/drivers/net/ppp/ppp_generic.c
> +++ b/drivers/net/ppp/ppp_generic.c
> @@ -2755,6 +2755,7 @@ static struct ppp *ppp_create_interface(struct net *net, int unit,
> */
> dev_net_set(dev, net);
>
> + rtnl_lock();
> mutex_lock(&pn->all_ppp_mutex);
>
> if (unit < 0) {
> @@ -2785,7 +2786,7 @@ static struct ppp *ppp_create_interface(struct net *net, int unit,
> ppp->file.index = unit;
> sprintf(dev->name, "ppp%d", unit);
>
> - ret = register_netdev(dev);
> + ret = register_netdevice(dev);
> if (ret != 0) {
> unit_put(&pn->units_idr, unit);
> netdev_err(ppp->dev, "PPP: couldn't register device %s (%d)\n",
> @@ -2797,6 +2798,7 @@ static struct ppp *ppp_create_interface(struct net *net, int unit,
>
> atomic_inc(&ppp_unit_count);
> mutex_unlock(&pn->all_ppp_mutex);
> + rtnl_unlock();
>
> *retp = 0;
> return ppp;

I have adapted your patch against Linux v4.2.1 and it fixes the issue for me.
Testcase:
1. Stop network-manager and unload "PPP Deflate Compression module".
2. Reload module and restart NM.
( No call-traces pointing to ppp. )

Do you mind to send a proper patch with subject-line and commit-message?
Can you embed the Fixes-tag and give credits like Reported-by/Tested-by?

Thanks.

- Sedat -
From d4ace3e00129687b680977ecc5ea4c9a03e35b63 Mon Sep 17 00:00:00 2001
From: Sedat Dilek <sedat.dilek@gmail.com>
Date: Wed, 23 Sep 2015 22:33:31 +0200
Subject: [PATCH] ppp: Fix circular locking dependency

---
drivers/net/ppp/ppp_generic.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c
index fa8f5046afe9..487be20b6b12 100644
--- a/drivers/net/ppp/ppp_generic.c
+++ b/drivers/net/ppp/ppp_generic.c
@@ -2742,6 +2742,7 @@ static struct ppp *ppp_create_interface(struct net *net, int unit,
*/
dev_net_set(dev, net);

+ rtnl_lock();
mutex_lock(&pn->all_ppp_mutex);

if (unit < 0) {
@@ -2772,7 +2773,7 @@ static struct ppp *ppp_create_interface(struct net *net, int unit,
ppp->file.index = unit;
sprintf(dev->name, "ppp%d", unit);

- ret = register_netdev(dev);
+ ret = register_netdevice(dev);
if (ret != 0) {
unit_put(&pn->units_idr, unit);
netdev_err(ppp->dev, "PPP: couldn't register device %s (%d)\n",
@@ -2784,6 +2785,7 @@ static struct ppp *ppp_create_interface(struct net *net, int unit,

atomic_inc(&ppp_unit_count);
mutex_unlock(&pn->all_ppp_mutex);
+ rtnl_unlock();

*retp = 0;
return ppp;
--
2.5.3
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