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Re: kern/53043: deadlock on evbarm/TEGRA with netbsd-8
The following reply was made to PR kern/53043; it has been noted by GNATS.
From: Ryota Ozaki <ozaki-r%netbsd.org@localhost>
To: Nick Hudson <skrll%netbsd.org@localhost>
Cc: "gnats-bugs%NetBSD.org@localhost" <gnats-bugs%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: Fri, 23 Feb 2018 18:02:02 +0900
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,
>> 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:
>> Note that I gave up moving softnet_lock to doifioctl because it
>> just introduced other deadlocks and was more problematic.
> 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.
I think we should think of a way to enable NET_MPSAFE coexisting with
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