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SubjectRe: net/core: BUG in unregister_netdevice_many
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On 21/04/17 20:42, Linus Torvalds wrote:
> On Fri, Apr 21, 2017 at 10:25 AM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
>>
>> I'm assuming that the real cause is simply that "dev->reg_state" ends
>> up being NETREG_UNREGISTERING or something. Maybe the BUG_ON() could
>> be just removed, and replaced by the previous warning about
>> NETREG_UNINITIALIZED.
>>
>> Something like the attached (TOTALLY UNTESTED) patch.
>
> .. might as well test it.
>
> That patch doesn't fix the problem, but it does show that yes, it was
> NETREG_UNREGISTERING:
>
> unregister_netdevice: device pim6reg/ffff962dc4606000 was not registered (2)
>
> but then immediately afterwards we get
>
> general protection fault: 0000 [#1] SMP
> Workqueue: netns cleanup_net
> RIP: 0010:dev_shutdown+0xe/0xc0
> Call Trace:
> rollback_registered_many+0x2a5/0x440
> unregister_netdevice_many+0x1e/0xb0
> default_device_exit_batch+0x145/0x170
>
> which is due to a
>
> mov 0x388(%rdi),%eax
>
> where %rdi is 0xdead000000000090. That is at the very beginning of
> dev_shutdown, it's "dev" itself that has that value, so it comes from
> (_another_) invocation of rollback_registered_many(), when it does
> that
>
> list_for_each_entry(dev, head, unreg_list) {
>
> so it seems to be a case of another "list_del() leaves list in bad
> state", and it was the added test for "dev->reg_state !=
> NETREG_REGISTERED" that did that
>
> list_del(&dev->unreg_list);
>
> and left random contents in the unreg_list.
>
> So that "handle error case" was almost certainly just buggy too.
>
> And the bug seems to be that we're trying to unregister a netdevice
> that has already been unregistered.
>
> Over to Eric and networking people. This oops is user-triggerable, and
> leaves the machine in a bad state (the original BUG_ON() and the new
> GP fault both happen while holding the RTNL, so networking is not
> healthy afterwards.
>
> Linus
>

Right, I've already posted a patch for ip6mr that should fix the issue.
CCed you and LKML just now.

Thanks,
Nik

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