linux-kernel - 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 23:21:50 +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 10:46 PM, Sedat Dilek <sedat.dilek@...il.com> wrote:
> 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.
>

Do not forget CC-stable Tag, too.

     Cc: stable@...r.kernel.org# v4.2+

See attached patch for-4.3.

- sed@ -

[1] http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/SubmittingPatches#n187
[2] http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/SubmittingPatches#n297

View attachment "0001-ppp-Fix-circular-locking-dependency-in-ppp_create_in.patch" of type "text/x-patch" (1722 bytes)