Hi Mathias, On 12 December 2016 at 23:52, Mathias Nyman <mathias.nyman@xxxxxxxxxxxxxxx> wrote: > On 05.12.2016 09:51, Baolin Wang wrote: >> >> If a command event is found on the event ring during an interrupt, >> we need to stop the command timer with del_timer(). Since del_timer() >> can fail if the timer is running and waiting on the xHCI lock, then >> it maybe get the wrong timeout command in xhci_handle_command_timeout() >> if host fetched a new command and updated the xhci->current_cmd in >> handle_cmd_completion(). For this situation, we need a way to signal >> to the command timer that everything is fine and it should exit. > > > Ah, right, this could actually happen. > >> >> >> We should introduce a counter (xhci->current_cmd_pending) for the number >> of pending commands. If we need to cancel the command timer and >> del_timer() >> succeeds, we decrement the number of pending commands. If del_timer() >> fails, >> we leave the number of pending commands alone. >> >> For handling timeout command, in xhci_handle_command_timeout() we will >> check >> the counter after decrementing it, if the counter >> (xhci->current_cmd_pending) >> is 0, which means xhci->current_cmd is the right timeout command. If the >> counter (xhci->current_cmd_pending) is greater than 0, which means current >> timeout command has been handled by host and host has fetched new command >> as >> xhci->current_cmd, then just return and wait for new current command. > > > A counter like this could work. > > Writing the abort bit can generate either ABORT+STOP, or just STOP > event, this seems to cover both. > > quick check, case 1: timeout and cmd completion at the same time. > > cpu1 cpu2 > > queue_command(first), p++ (=1) > queue_command(more), > --completion irq fires-- -- timer times out at same time-- > handle_cmd_completion() handle_cmd_timeout(),) > lock(xhci_lock ) spin_on(xhci_lock) > del_timer() fail, p (=1, nochange) > cur_cmd = list_next(), p++ (=2) > unlock(xhci_lock) > lock(xhci_lock) > p-- (=1) > if (p > 0), exit > OK works > > case 2: normal timeout case with ABORT+STOP, no race. > > cpu1 cpu2 > > queue_command(first), p++ (=1) > queue_command(more), > handle_cmd_timeout() > p-- (P=0), don't exit > mod_timer(), p++ (P=1) > write_abort_bit() > handle_cmd_comletion(ABORT) > del_timer(), ok, p-- (p = 0) > handle_cmd_completion(STOP) > del_timer(), fail, (P=0) > handle_stopped_cmd_ring() > cur_cmd = list_next(), p++ (=1) > mod_timer() > > OK, works, and same for just STOP case, with the only difference that > during handle_cmd_completion(STOP) p is decremented (p--) Yes, that's the cases what I want to handle, thanks for your explicit explanation. > > So unless there is a way to find out if cur_cmd is valid in command timeout > in command timeout with the help of existing flags and lists this would be a > working > solution. > > -Mathias > -- Baolin.wang Best Regards -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
