Hello, I'm consistently observing kernel warnings related to Mass Storage USB Gadget de-initialization flow. After investigation I believe that I've found root cause of these warnings, however I'm unable to estimate the impact. I would like to put the issue into discussion about possible side-effects. My usage model is to emulate file system using f_mass_storage gadget. Whenever I pull the USB cable out I see warning related to "dwc2_hsotg_init_fifo" which is commented in the following way: "/* Reset fifo map if not correctly cleared during previous session */". Assumption I've made were the following: 1) disconnect handler notifies all gadgets with call_gadget(.., disconnect) 2) gadgets are then responsible to clear the ep fifos with usb_ep_disable() 3) disconnect handler initializes the fifo maps to clear state Unfortunately in my case the warning occurs every time when using f_mass_storage gadget. By comparison with f_hid gadget I've come up with conclusion that it's caused by race condition in the way the "disable" flow is implemented in mass storage. "Correct" flow implemented by HID gadget is the following: * dwc2_hsotg_irq (USBRst) ** dwc2_hsotg_disconnect *** call_gadget(disconnect) **** hidg_disable ***** usb_ep_disable // fifos utilized by device are cleared in fifo_map ** dwc_hsotg_core_init_disconnected *** dwc2_hsotg_init_fifo // fifo_map is empty - no warning here By comparison here is flow observed in Mass Storage gadget. Race condition is introduced by utilizing separate worker thread to handle events: THREAD #1 * dwc2_hsotg_irq (USBRst) ** dwc2_hsotg_disconnect *** call_gadget(disconnect) **** fsg_disable() ***** raise_exception(FSG_STATE_CONFIG_CHANGE) // Race between Thread #1 and Thread #2 starts here. ** dwc_hsotg_core_init_disconnected *** dwc2_hsotg_init_fifo // fifo_map is object of the race between this function, and call to usb_ep_disable() THREAD #2 * handle_exception(FSG_STATE_CONFIG_CHANGE) ** do_set_interface(NULL) *** usb_ep_disable() My questions are the following: - is this known issue? - is it risky? What are possible outcomes? - If this race condition is dangerous what would be proper fix ? Should fsg_disable() call be blocked until handle_exception() finishes the cleanup? I know that it's just a WA for "misaligned" Mass Storage gadget architecture, but are there alternatives? I would really appreciate professional insight on that matter, Regards, Adrian
