Static analysis: Improve DAD deletion code

[jtl]

Summary

I ran clang's static analyzer over the kernel sources. It identified some concerns with the way DAD entries were removed from the DAD queue.

This change adds a flag to the DAD entry to indicate whether it is currently on the queue. This prevents accidentally doubly-removing a DAD entry from the queue, while also simplifying some of the logic in nd6_dad_stop().

Sponsored by: Netflix
MFC after: 2 weeks

[jtl]

Can someone please review this? This has been outstanding for a while...

[vangyzen]

sys/netinet6/nd6_nbr.c

1149 ↗

(On Diff #28874)

I don't like the refcount asymmetry between add() and del(), but add() is only called in one place, and this predates your change, so I'm just complaining in your general direction. :)

1307 ↗

(On Diff #28874)

At first, I didn't understand whose reference this is releasing. Maybe it's worth a comment, like

/* Release this function's reference, acquired by nd6_dad_find(). */

On the other hand, anyone who works in this code will need to understand this behavior, so maybe the comment is superfluous. Your call.

[jtl]

sys/netinet6/nd6_nbr.c

1149 ↗

(On Diff #28874)

Agreed. :-)

1307 ↗

(On Diff #28874)

Seems reasonable. I can add the comment.