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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 <>
To: "" <>
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.

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