Sooo... I think I found what's going on with some of the issues triggering things like usb_composite_setup_continue: Unexpected call Or possibly gadget: common->fsg is NULL in fsg_setup at 489 But I mostly tracked down the former. Fundamentally, it boils down to the storage going through multiple attempts at FSG_STATE_CONFIG_CHANGE too quickly. In my case: - The hub port gets reset, this eventually calls fsg_disable - In the middle of handle_exception, we get a fsg_set_alt(), after common->state is set back to FSG_STATE_NORMAL and before we get to call do_set_interface (or inside it). What happens is that not only new_fsg is indeterminate and possibly racy (maybe not a huge deal per-se), but we end up in that interesting situation where the handle_exception caused by fsg_disable ends up applying "new_fsg" *and* calling usb_composite_setup_continue because it sees new_fsg being set by fsg_set_alt. But *then*, fsg_set_alt() also queues up a new exception. So we come back a second time around. We call do_set_interface() again, which resets everything for no reason, re-established the fsg and ... we call usb_composite_setup_continue() again, this time completely at the wrong time since there's nothing to continue. I think the right fix is to replace that racy exception crap with a little queue so we remove those races. In the meantime however, I think the simpler patch that I'll send as a reply to this works around it, provided the host doesn't do multiple set_alt too quickly. The latter could be handled by setting new_fsg with the lock used for the state, and reading it from that same lock. But I haven't observed that problem in practice. With this patch, I can now unplug & replug on my host solidly, this wasn't the case before. Cheers, Ben.
