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Re: [PATCH net] ip6mr: fix notification device destruction

Started byNikolay Aleksandrov <nikolay@cumulusnetworks.com>
First post2017-04-21 20:40 +0200
Last post2017-04-21 22:00 +0200
Articles 7 — 3 participants

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  Re: [PATCH net] ip6mr: fix notification device destruction Nikolay Aleksandrov <nikolay@cumulusnetworks.com> - 2017-04-21 20:40 +0200
    Re: [PATCH net] ip6mr: fix notification device destruction Andrey Konovalov <andreyknvl@google.com> - 2017-04-21 20:50 +0200
    Re: [PATCH net] ip6mr: fix notification device destruction David Miller <davem@davemloft.net> - 2017-04-21 21:40 +0200
      Re: [PATCH net] ip6mr: fix notification device destruction David Miller <davem@davemloft.net> - 2017-04-21 22:00 +0200
      Re: [PATCH net] ip6mr: fix notification device destruction Nikolay Aleksandrov <nikolay@cumulusnetworks.com> - 2017-04-21 22:00 +0200
        Re: [PATCH net] ip6mr: fix notification device destruction Nikolay Aleksandrov <nikolay@cumulusnetworks.com> - 2017-04-21 22:00 +0200
        Re: [PATCH net] ip6mr: fix notification device destruction David Miller <davem@davemloft.net> - 2017-04-21 22:00 +0200

#1628460 — Re: [PATCH net] ip6mr: fix notification device destruction

FromNikolay Aleksandrov <nikolay@cumulusnetworks.com>
Date2017-04-21 20:40 +0200
SubjectRe: [PATCH net] ip6mr: fix notification device destruction
Message-ID<tyLDk-LM-23@gated-at.bofh.it>
On 21/04/17 20:42, Nikolay Aleksandrov wrote:
> Andrey Konovalov reported a BUG caused by the ip6mr code which is caused
> because we call unregister_netdevice_many for a device that is already
> being destroyed. In IPv4's ipmr that has been resolved by two commits
> long time ago by introducing the "notify" parameter to the delete
> function and avoiding the unregister when called from a notifier, so
> let's do the same for ip6mr.
> 
> The trace from Andrey:
> ------------[ cut here ]------------
> kernel BUG at net/core/dev.c:6813!
> invalid opcode: 0000 [#1] SMP KASAN
> Modules linked in:
> CPU: 1 PID: 1165 Comm: kworker/u4:3 Not tainted 4.11.0-rc7+ #251
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs
> 01/01/2011
> Workqueue: netns cleanup_net
> task: ffff880069208000 task.stack: ffff8800692d8000
> RIP: 0010:rollback_registered_many+0x348/0xeb0 net/core/dev.c:6813
> RSP: 0018:ffff8800692de7f0 EFLAGS: 00010297
> RAX: ffff880069208000 RBX: 0000000000000002 RCX: 0000000000000001
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff88006af90569
> RBP: ffff8800692de9f0 R08: ffff8800692dec60 R09: 0000000000000000
> R10: 0000000000000006 R11: 0000000000000000 R12: ffff88006af90070
> R13: ffff8800692debf0 R14: dffffc0000000000 R15: ffff88006af90000
> FS:  0000000000000000(0000) GS:ffff88006cb00000(0000)
> knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fe7e897d870 CR3: 00000000657e7000 CR4: 00000000000006e0
> Call Trace:
>  unregister_netdevice_many.part.105+0x87/0x440 net/core/dev.c:7881
>  unregister_netdevice_many+0xc8/0x120 net/core/dev.c:7880
>  ip6mr_device_event+0x362/0x3f0 net/ipv6/ip6mr.c:1346
>  notifier_call_chain+0x145/0x2f0 kernel/notifier.c:93
>  __raw_notifier_call_chain kernel/notifier.c:394
>  raw_notifier_call_chain+0x2d/0x40 kernel/notifier.c:401
>  call_netdevice_notifiers_info+0x51/0x90 net/core/dev.c:1647
>  call_netdevice_notifiers net/core/dev.c:1663
>  rollback_registered_many+0x919/0xeb0 net/core/dev.c:6841
>  unregister_netdevice_many.part.105+0x87/0x440 net/core/dev.c:7881
>  unregister_netdevice_many net/core/dev.c:7880
>  default_device_exit_batch+0x4fa/0x640 net/core/dev.c:8333
>  ops_exit_list.isra.4+0x100/0x150 net/core/net_namespace.c:144
>  cleanup_net+0x5a8/0xb40 net/core/net_namespace.c:463
>  process_one_work+0xc04/0x1c10 kernel/workqueue.c:2097
>  worker_thread+0x223/0x19c0 kernel/workqueue.c:2231
>  kthread+0x35e/0x430 kernel/kthread.c:231
>  ret_from_fork+0x31/0x40 arch/x86/entry/entry_64.S:430
> Code: 3c 32 00 0f 85 70 0b 00 00 48 b8 00 02 00 00 00 00 ad de 49 89
> 47 78 e9 93 fe ff ff 49 8d 57 70 49 8d 5f 78 eb 9e e8 88 7a 14 fe <0f>
> 0b 48 8b 9d 28 fe ff ff e8 7a 7a 14 fe 48 b8 00 00 00 00 00
> RIP: rollback_registered_many+0x348/0xeb0 RSP: ffff8800692de7f0
> ---[ end trace e0b29c57e9b3292c ]---
> 
> Reported-by: Andrey Konovalov <andreyknvl@google.com>
> Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
> ---

+CC LKML and Linus

> Andrey could you please test with this patch applied ?
> I have run the reproducer locally and can no longer trigger the bug.
> I've made "notify" an int instead of a bool only to be closer to the ipmr
> code for easier future patches.
> 
>  net/ipv6/ip6mr.c | 13 ++++++-------
>  1 file changed, 6 insertions(+), 7 deletions(-)
> 
> diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
> index fb4546e80c82..374997d26488 100644
> --- a/net/ipv6/ip6mr.c
> +++ b/net/ipv6/ip6mr.c
> @@ -774,7 +774,8 @@ static struct net_device *ip6mr_reg_vif(struct net *net, struct mr6_table *mrt)
>   *	Delete a VIF entry
>   */
>  
> -static int mif6_delete(struct mr6_table *mrt, int vifi, struct list_head *head)
> +static int mif6_delete(struct mr6_table *mrt, int vifi, int notify,
> +		       struct list_head *head)
>  {
>  	struct mif_device *v;
>  	struct net_device *dev;
> @@ -820,7 +821,7 @@ static int mif6_delete(struct mr6_table *mrt, int vifi, struct list_head *head)
>  					     dev->ifindex, &in6_dev->cnf);
>  	}
>  
> -	if (v->flags & MIFF_REGISTER)
> +	if ((v->flags & MIFF_REGISTER) && !notify)
>  		unregister_netdevice_queue(dev, head);
>  
>  	dev_put(dev);
> @@ -1331,7 +1332,6 @@ static int ip6mr_device_event(struct notifier_block *this,
>  	struct mr6_table *mrt;
>  	struct mif_device *v;
>  	int ct;
> -	LIST_HEAD(list);
>  
>  	if (event != NETDEV_UNREGISTER)
>  		return NOTIFY_DONE;
> @@ -1340,10 +1340,9 @@ static int ip6mr_device_event(struct notifier_block *this,
>  		v = &mrt->vif6_table[0];
>  		for (ct = 0; ct < mrt->maxvif; ct++, v++) {
>  			if (v->dev == dev)
> -				mif6_delete(mrt, ct, &list);
> +				mif6_delete(mrt, ct, 1, NULL);
>  		}
>  	}
> -	unregister_netdevice_many(&list);
>  
>  	return NOTIFY_DONE;
>  }
> @@ -1552,7 +1551,7 @@ static void mroute_clean_tables(struct mr6_table *mrt, bool all)
>  	for (i = 0; i < mrt->maxvif; i++) {
>  		if (!all && (mrt->vif6_table[i].flags & VIFF_STATIC))
>  			continue;
> -		mif6_delete(mrt, i, &list);
> +		mif6_delete(mrt, i, 0, &list);
>  	}
>  	unregister_netdevice_many(&list);
>  
> @@ -1708,7 +1707,7 @@ int ip6_mroute_setsockopt(struct sock *sk, int optname, char __user *optval, uns
>  		if (copy_from_user(&mifi, optval, sizeof(mifi_t)))
>  			return -EFAULT;
>  		rtnl_lock();
> -		ret = mif6_delete(mrt, mifi, NULL);
> +		ret = mif6_delete(mrt, mifi, 0, NULL);
>  		rtnl_unlock();
>  		return ret;
>  
>

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#1628489

FromAndrey Konovalov <andreyknvl@google.com>
Date2017-04-21 20:50 +0200
Message-ID<tyLN0-Pg-31@gated-at.bofh.it>
In reply to#1628460
On Fri, Apr 21, 2017 at 8:30 PM, Nikolay Aleksandrov
<nikolay@cumulusnetworks.com> wrote:
> On 21/04/17 20:42, Nikolay Aleksandrov wrote:
>> Andrey Konovalov reported a BUG caused by the ip6mr code which is caused
>> because we call unregister_netdevice_many for a device that is already
>> being destroyed. In IPv4's ipmr that has been resolved by two commits
>> long time ago by introducing the "notify" parameter to the delete
>> function and avoiding the unregister when called from a notifier, so
>> let's do the same for ip6mr.

Hi Nikolay,

Your patch fixes BUG_ON() being triggered for me.

Tested-by: Andrey Konovalov <andreyknvl@google.com>

Thanks!

>>
>> The trace from Andrey:
>> ------------[ cut here ]------------
>> kernel BUG at net/core/dev.c:6813!
>> invalid opcode: 0000 [#1] SMP KASAN
>> Modules linked in:
>> CPU: 1 PID: 1165 Comm: kworker/u4:3 Not tainted 4.11.0-rc7+ #251
>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs
>> 01/01/2011
>> Workqueue: netns cleanup_net
>> task: ffff880069208000 task.stack: ffff8800692d8000
>> RIP: 0010:rollback_registered_many+0x348/0xeb0 net/core/dev.c:6813
>> RSP: 0018:ffff8800692de7f0 EFLAGS: 00010297
>> RAX: ffff880069208000 RBX: 0000000000000002 RCX: 0000000000000001
>> RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff88006af90569
>> RBP: ffff8800692de9f0 R08: ffff8800692dec60 R09: 0000000000000000
>> R10: 0000000000000006 R11: 0000000000000000 R12: ffff88006af90070
>> R13: ffff8800692debf0 R14: dffffc0000000000 R15: ffff88006af90000
>> FS:  0000000000000000(0000) GS:ffff88006cb00000(0000)
>> knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 00007fe7e897d870 CR3: 00000000657e7000 CR4: 00000000000006e0
>> Call Trace:
>>  unregister_netdevice_many.part.105+0x87/0x440 net/core/dev.c:7881
>>  unregister_netdevice_many+0xc8/0x120 net/core/dev.c:7880
>>  ip6mr_device_event+0x362/0x3f0 net/ipv6/ip6mr.c:1346
>>  notifier_call_chain+0x145/0x2f0 kernel/notifier.c:93
>>  __raw_notifier_call_chain kernel/notifier.c:394
>>  raw_notifier_call_chain+0x2d/0x40 kernel/notifier.c:401
>>  call_netdevice_notifiers_info+0x51/0x90 net/core/dev.c:1647
>>  call_netdevice_notifiers net/core/dev.c:1663
>>  rollback_registered_many+0x919/0xeb0 net/core/dev.c:6841
>>  unregister_netdevice_many.part.105+0x87/0x440 net/core/dev.c:7881
>>  unregister_netdevice_many net/core/dev.c:7880
>>  default_device_exit_batch+0x4fa/0x640 net/core/dev.c:8333
>>  ops_exit_list.isra.4+0x100/0x150 net/core/net_namespace.c:144
>>  cleanup_net+0x5a8/0xb40 net/core/net_namespace.c:463
>>  process_one_work+0xc04/0x1c10 kernel/workqueue.c:2097
>>  worker_thread+0x223/0x19c0 kernel/workqueue.c:2231
>>  kthread+0x35e/0x430 kernel/kthread.c:231
>>  ret_from_fork+0x31/0x40 arch/x86/entry/entry_64.S:430
>> Code: 3c 32 00 0f 85 70 0b 00 00 48 b8 00 02 00 00 00 00 ad de 49 89
>> 47 78 e9 93 fe ff ff 49 8d 57 70 49 8d 5f 78 eb 9e e8 88 7a 14 fe <0f>
>> 0b 48 8b 9d 28 fe ff ff e8 7a 7a 14 fe 48 b8 00 00 00 00 00
>> RIP: rollback_registered_many+0x348/0xeb0 RSP: ffff8800692de7f0
>> ---[ end trace e0b29c57e9b3292c ]---
>>
>> Reported-by: Andrey Konovalov <andreyknvl@google.com>
>> Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
>> ---
>
> +CC LKML and Linus
>
>> Andrey could you please test with this patch applied ?
>> I have run the reproducer locally and can no longer trigger the bug.
>> I've made "notify" an int instead of a bool only to be closer to the ipmr
>> code for easier future patches.
>>
>>  net/ipv6/ip6mr.c | 13 ++++++-------
>>  1 file changed, 6 insertions(+), 7 deletions(-)
>>
>> diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
>> index fb4546e80c82..374997d26488 100644
>> --- a/net/ipv6/ip6mr.c
>> +++ b/net/ipv6/ip6mr.c
>> @@ -774,7 +774,8 @@ static struct net_device *ip6mr_reg_vif(struct net *net, struct mr6_table *mrt)
>>   *   Delete a VIF entry
>>   */
>>
>> -static int mif6_delete(struct mr6_table *mrt, int vifi, struct list_head *head)
>> +static int mif6_delete(struct mr6_table *mrt, int vifi, int notify,
>> +                    struct list_head *head)
>>  {
>>       struct mif_device *v;
>>       struct net_device *dev;
>> @@ -820,7 +821,7 @@ static int mif6_delete(struct mr6_table *mrt, int vifi, struct list_head *head)
>>                                            dev->ifindex, &in6_dev->cnf);
>>       }
>>
>> -     if (v->flags & MIFF_REGISTER)
>> +     if ((v->flags & MIFF_REGISTER) && !notify)
>>               unregister_netdevice_queue(dev, head);
>>
>>       dev_put(dev);
>> @@ -1331,7 +1332,6 @@ static int ip6mr_device_event(struct notifier_block *this,
>>       struct mr6_table *mrt;
>>       struct mif_device *v;
>>       int ct;
>> -     LIST_HEAD(list);
>>
>>       if (event != NETDEV_UNREGISTER)
>>               return NOTIFY_DONE;
>> @@ -1340,10 +1340,9 @@ static int ip6mr_device_event(struct notifier_block *this,
>>               v = &mrt->vif6_table[0];
>>               for (ct = 0; ct < mrt->maxvif; ct++, v++) {
>>                       if (v->dev == dev)
>> -                             mif6_delete(mrt, ct, &list);
>> +                             mif6_delete(mrt, ct, 1, NULL);
>>               }
>>       }
>> -     unregister_netdevice_many(&list);
>>
>>       return NOTIFY_DONE;
>>  }
>> @@ -1552,7 +1551,7 @@ static void mroute_clean_tables(struct mr6_table *mrt, bool all)
>>       for (i = 0; i < mrt->maxvif; i++) {
>>               if (!all && (mrt->vif6_table[i].flags & VIFF_STATIC))
>>                       continue;
>> -             mif6_delete(mrt, i, &list);
>> +             mif6_delete(mrt, i, 0, &list);
>>       }
>>       unregister_netdevice_many(&list);
>>
>> @@ -1708,7 +1707,7 @@ int ip6_mroute_setsockopt(struct sock *sk, int optname, char __user *optval, uns
>>               if (copy_from_user(&mifi, optval, sizeof(mifi_t)))
>>                       return -EFAULT;
>>               rtnl_lock();
>> -             ret = mif6_delete(mrt, mifi, NULL);
>> +             ret = mif6_delete(mrt, mifi, 0, NULL);
>>               rtnl_unlock();
>>               return ret;
>>
>>
>
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#1628546

FromDavid Miller <davem@davemloft.net>
Date2017-04-21 21:40 +0200
Message-ID<tyMzo-1ke-5@gated-at.bofh.it>
In reply to#1628460
From: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Date: Fri, 21 Apr 2017 21:30:42 +0300

> On 21/04/17 20:42, Nikolay Aleksandrov wrote:
>> Andrey Konovalov reported a BUG caused by the ip6mr code which is caused
>> because we call unregister_netdevice_many for a device that is already
>> being destroyed. In IPv4's ipmr that has been resolved by two commits
>> long time ago by introducing the "notify" parameter to the delete
>> function and avoiding the unregister when called from a notifier, so
>> let's do the same for ip6mr.
 ...
> +CC LKML and Linus

Applied, thanks Nikolay and thanks Andrey for the report and testing.

Nikolay, how far does this bug go back?

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#1628564

FromDavid Miller <davem@davemloft.net>
Date2017-04-21 22:00 +0200
Message-ID<tyMSJ-1qO-9@gated-at.bofh.it>
In reply to#1628546
From: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Date: Fri, 21 Apr 2017 22:56:26 +0300

> On 21/04/17 22:50, Nikolay Aleksandrov wrote:
>> On 21/04/17 22:36, David Miller wrote:
>>> From: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
>>> Date: Fri, 21 Apr 2017 21:30:42 +0300
>>>
>>>> On 21/04/17 20:42, Nikolay Aleksandrov wrote:
>>>>> Andrey Konovalov reported a BUG caused by the ip6mr code which is caused
>>>>> because we call unregister_netdevice_many for a device that is already
>>>>> being destroyed. In IPv4's ipmr that has been resolved by two commits
>>>>> long time ago by introducing the "notify" parameter to the delete
>>>>> function and avoiding the unregister when called from a notifier, so
>>>>> let's do the same for ip6mr.
>>>  ...
>>>> +CC LKML and Linus
>>>
>>> Applied, thanks Nikolay and thanks Andrey for the report and testing.
>>>
>>> Nikolay, how far does this bug go back?
>>>
>> 
>> Good question, AFAICS since ip6mr exists because it was copied from ipmr:
>> commit 7bc570c8b4f7
>> Author: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
>> Date:   Thu Apr 3 09:22:53 2008 +0900
>> 
>>     [IPV6] MROUTE: Support multicast forwarding.
>> 
>> 
> 
> Oops no, my bad. That wouldn't cause it to BUG because it was already removed by mif6_delete
> earlier. So since it can be destroyed by a netns exiting, currently I don't see any other
> way which is outside of ip6mr for destroying that device.
> 
> That should be:
> commit 8229efdaef1e
> Author: Benjamin Thery <benjamin.thery@bull.net>
> Date:   Wed Dec 10 16:30:15 2008 -0800
> 
>     netns: ip6mr: enable namespace support in ipv6 multicast forwarding code
> 
> 
> Which allowed the notifier to be executed for pimreg devices in other network namespaces.

That still makes it -stable material as far as I'm concerned.

Thanks again! :)

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#1628565

FromNikolay Aleksandrov <nikolay@cumulusnetworks.com>
Date2017-04-21 22:00 +0200
Message-ID<tyMSJ-1qO-11@gated-at.bofh.it>
In reply to#1628546
On 21/04/17 22:36, David Miller wrote:
> From: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
> Date: Fri, 21 Apr 2017 21:30:42 +0300
> 
>> On 21/04/17 20:42, Nikolay Aleksandrov wrote:
>>> Andrey Konovalov reported a BUG caused by the ip6mr code which is caused
>>> because we call unregister_netdevice_many for a device that is already
>>> being destroyed. In IPv4's ipmr that has been resolved by two commits
>>> long time ago by introducing the "notify" parameter to the delete
>>> function and avoiding the unregister when called from a notifier, so
>>> let's do the same for ip6mr.
>  ...
>> +CC LKML and Linus
> 
> Applied, thanks Nikolay and thanks Andrey for the report and testing.
> 
> Nikolay, how far does this bug go back?
> 

Good question, AFAICS since ip6mr exists because it was copied from ipmr:
commit 7bc570c8b4f7
Author: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Date:   Thu Apr 3 09:22:53 2008 +0900

    [IPV6] MROUTE: Support multicast forwarding.

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#1628566

FromNikolay Aleksandrov <nikolay@cumulusnetworks.com>
Date2017-04-21 22:00 +0200
Message-ID<tyMSJ-1qO-13@gated-at.bofh.it>
In reply to#1628565
On 21/04/17 22:50, Nikolay Aleksandrov wrote:
> On 21/04/17 22:36, David Miller wrote:
>> From: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
>> Date: Fri, 21 Apr 2017 21:30:42 +0300
>>
>>> On 21/04/17 20:42, Nikolay Aleksandrov wrote:
>>>> Andrey Konovalov reported a BUG caused by the ip6mr code which is caused
>>>> because we call unregister_netdevice_many for a device that is already
>>>> being destroyed. In IPv4's ipmr that has been resolved by two commits
>>>> long time ago by introducing the "notify" parameter to the delete
>>>> function and avoiding the unregister when called from a notifier, so
>>>> let's do the same for ip6mr.
>>  ...
>>> +CC LKML and Linus
>>
>> Applied, thanks Nikolay and thanks Andrey for the report and testing.
>>
>> Nikolay, how far does this bug go back?
>>
> 
> Good question, AFAICS since ip6mr exists because it was copied from ipmr:
> commit 7bc570c8b4f7
> Author: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
> Date:   Thu Apr 3 09:22:53 2008 +0900
> 
>     [IPV6] MROUTE: Support multicast forwarding.
> 
> 

Oops no, my bad. That wouldn't cause it to BUG because it was already removed by mif6_delete
earlier. So since it can be destroyed by a netns exiting, currently I don't see any other
way which is outside of ip6mr for destroying that device.

That should be:
commit 8229efdaef1e
Author: Benjamin Thery <benjamin.thery@bull.net>
Date:   Wed Dec 10 16:30:15 2008 -0800

    netns: ip6mr: enable namespace support in ipv6 multicast forwarding code


Which allowed the notifier to be executed for pimreg devices in other network namespaces.

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#1628568

FromDavid Miller <davem@davemloft.net>
Date2017-04-21 22:00 +0200
Message-ID<tyMSK-1qO-25@gated-at.bofh.it>
In reply to#1628565
From: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Date: Fri, 21 Apr 2017 22:50:35 +0300

> On 21/04/17 22:36, David Miller wrote:
>> From: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
>> Date: Fri, 21 Apr 2017 21:30:42 +0300
>> 
>>> On 21/04/17 20:42, Nikolay Aleksandrov wrote:
>>>> Andrey Konovalov reported a BUG caused by the ip6mr code which is caused
>>>> because we call unregister_netdevice_many for a device that is already
>>>> being destroyed. In IPv4's ipmr that has been resolved by two commits
>>>> long time ago by introducing the "notify" parameter to the delete
>>>> function and avoiding the unregister when called from a notifier, so
>>>> let's do the same for ip6mr.
>>  ...
>>> +CC LKML and Linus
>> 
>> Applied, thanks Nikolay and thanks Andrey for the report and testing.
>> 
>> Nikolay, how far does this bug go back?
>> 
> 
> Good question, AFAICS since ip6mr exists because it was copied from ipmr:
> commit 7bc570c8b4f7
> Author: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
> Date:   Thu Apr 3 09:22:53 2008 +0900
> 
>     [IPV6] MROUTE: Support multicast forwarding.

Ok will queue it up for -stable.

Thanks.

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