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--) 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 -- 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
