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

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

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,
 >> 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