Re: kern/53043: deadlock on evbarm/TEGRA with netbsd-8

[Ryota Ozaki <ozaki-r%netbsd.org@localhost>]

On Fri, Feb 23, 2018 at 5:59 AM, Nick Hudson <skrll%netbsd.org@localhost> wrote:
> On 02/22/18 08:25, Ryota Ozaki wrote:
>>
>> The following reply was made to PR kern/53043; it has been noted by GNATS.
>>
>> From: Ryota Ozaki <ozaki-r%netbsd.org@localhost>
>> To: "gnats-bugs%NetBSD.org@localhost" <gnats-bugs%netbsd.org@localhost>
>> Cc: kern-bug-people%netbsd.org@localhost, gnats-admin%netbsd.org@localhost,
>> netbsd-bugs%netbsd.org@localhost
>> Subject: Re: kern/53043: deadlock on evbarm/TEGRA with netbsd-8
>> Date: Thu, 22 Feb 2018 17:24:13 +0900
>>
>>   This is a deadlock that occurs between softnet_lock and IFNET_LOCK;
>>   the locks can be held in different orders.
>>     softnet_lock in in6_control (and in_control) had been introduced to
>>   address PR 51356 that was a race condition between ioctls and packet
>>   inputs and forwarding (ipintr and ip6intr). However holding it
>>   in6_control and in_control was not a good idea because softnet_lock
>>   should be basically held at the very beginning of call paths to comply
>>   the locking order and the functions were in the middle of call paths.
>>     I think we have two options to solve the issue:
>>   (1) Give up relying on softnet_lock to protect the network stack and
>>       remove softnet_lock from in6_control/in_control and add some
>>       KERNEL_LOCK to the network stack, e.g., ipintr and ip6intr.
>>   (2) Just get rid of softnet_lock from in6_control/in_control.
>>     (1) is safer than (2) but add some performance penalty. (2) sounds
>>   awful but the situation is the same as netbsd-7 and netbsd-6, i.e.,
>>   it's enough safe in practice...
>>     A patch for (1) is here:
>> http://www.netbsd.org/~ozaki-r/fix-pr53043.diff
>>     Note that I gave up moving softnet_lock to doifioctl because it
>>   just introduced other deadlocks and was more problematic.
>>     Comments?
>>
>
>
> I think 1) is the only real option for now. Hopefully someone can address
> finer grained locking soon.
>
> I tested your patch and my tegra can now complete an atf-run.

Thanks.

I think we should think of a way to enable NET_MPSAFE coexisting with
non-MP-safe components...

  ozaki-r