bus: Take the topolock in driver_module_handler()

[imp]

Summary

And sprinkler some asserts. Right now all module handlers are called
with Giant, but I'd like to drop that so push the newbus locking one
step further.

Sponsored by: Netflix

[jhb]

I haven't yet looked at Mark's changes to see how they conflict.

sys/kern/subr_bus.c

5273

Arguably, we should only create the devclass for MOD_LOAD (and pass false instead of true for MOD_UNLOAD and MOD_QUIESCE), and we should perhaps run the chained handlers not under the topo_lock (requiring the chained handlers to manage their own locking). You could fix both of those by pushing the devclass_find_internal() down into each case below, but that that's kind of tedious. This is probably fine for now.

[imp]

sys/kern/subr_bus.c

5273

Agreed. I'll do that as new patches in the series.

[markj]

This change depends on D53451, not the other way around. If you commit just this one, the devclass_find_internal() assertion will fail in some cases.