On Wed, 6 May 2015, yoma sophian wrote: > hi all: > I am writing a thread and it will call sd_check_events per 1 second. Is your thread freezable? It should be, if it is going to do I/O. > 1. before system goes to hibernate, the thread works fine > > 2. system hibernate and restore back. > > 3. udev->state will keep USB_STATE_SUSPENDED before finish_port_resume > > 4. during above 2) and 3) sd_check_events keep polling but get > transport error and call usb_stor_port_reset. > since udev->state is USB_STATE_SUSPENDED, the usb_stor_port_reset > will fail due to unable lock device for reset (error = -113) That's why your thread needs to be freezable. Also, it sounds like you haven't considered Runtime PM. A USB mass-storage device can be set to go into runtime suspend after (for example) 5 seconds of inactivity. If your new thread calls sd_check_events every second then the device will never have 5 seconds of inactivity, so it will never go into runtime suspend. This means your thread will waste energy. Besides, the kernel already contains a thread that calls sd_check_events periodically. Why do you need to write a new one? > 5. in finish_port_resume, it first change udev->state as > USB_STATE_CONFIGURED or USB_STATE_ADDRESS. then call > usb_reset_and_verify_device like below: > usb_set_device_state(udev, udev->actconfig > ? USB_STATE_CONFIGURED > : USB_STATE_ADDRESS); > > /* 10.5.4.5 says not to reset a suspended port if the attached > * device is enabled for remote wakeup. Hence the reset > * operation is carried out here, after the port has been > * resumed. > */ > if (udev->reset_resume) > retry_reset_resume: > status = usb_reset_and_verify_device(udev); > > 6. usb_reset_and_verify_device will call hub_port_init > > 7. usb_reset_and_verify_device will call descriptors_changed, > > 8. if sd_check_events polling again in during 6) and 7), > descriptors_changed may return true and report port resume fail. > > My questions are: > a. is there any system flag such suspend/resume in scsi layer for > checking before sending command to downlayer driver, such as usb. I don't know of any. In general, the kernel is designed so that no SCSI commands will be sent while the system is in suspend or hibernation, so no checking is needed. > b. shall we add other flag in usb_stor_port_reset to make sure above > race condition will not happen? No. You should fix your thread (or get rid of it and use the existing kernel thread instead). Alan Stern -- 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
