netdev - Re: [Linux 4.2-rc8+...v4.3-rc2] REGRESSION: ppp: circular locking dependency detected: [pppd] ppp_dev_uninit()

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Date:	Wed, 23 Sep 2015 22:46:00 +0200
From:	Sedat Dilek <sedat.dilek@...il.com>
To:	Guillaume Nault <g.nault@...halink.fr>
Cc:	"David S. Miller" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [Linux 4.2-rc8+...v4.3-rc2] REGRESSION: ppp: circular locking
 dependency detected: [pppd] ppp_dev_uninit() | rtnl_lock()

On Wed, Sep 23, 2015 at 12:38 PM, Guillaume Nault <g.nault@...halink.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 -

View attachment "0001-ppp-Fix-circular-locking-dependency-linux-4-2-1.patch" of type "text/x-patch" (1229 bytes)