On 11/25/2013 09:41 PM, Alan Stern wrote: > On Mon, 25 Nov 2013, Daniel Mack wrote: > >>>>> What if you have a mounted file system on a pendrive ? Should we allow >>>>> suspend in that case ? >>>> >>>> Well, I would have expected that, but in fact, the opposite is true. >>>> With 3.12, mounting a filesystem on a USB media and accessing it after >>>> resume was exactly my test case, and it worked just fine with that patch. >>> >>> so you had a mounted file system, suspend, resume, it was still mounted? >> >> Yes, exactly. >> >>> or did it reenumerate and you remounted it ? >> >> No, it did not reenumerate, but the core did a reset on it. See the >> following log. > > ... >> [ 32.030792] usb 1-1: reset high-speed USB device number 2 using >> musb-hdrc <<<< ! > > Like I said, you get a reset-resume. Yup. We can't avoid losing VBUS on this platform, and even if we could, we wouldn't want that, in order to save as much power as possible. >>> Try to do the same with transfers in flight, it's likely to corrupt your >>> file system. > > It's not so easy to suspend a system with USB mass-storage transfers in > flight. For one thing, userspace gets frozen before the suspend > starts, so there's nothing to initiate new I/O requests (except perhaps > for dirty-block writebacks). > > Also, the child SCSI device gets suspended before the USB device, so > its I/O queue stops running. In addition, the usb-storage suspend > routine and the main I/O thread are mutually exclusive (they both grab > the private mutex), so a suspend can't occur while a SCSI command is > underway. Thanks Alan for the explanation. That was my understanding as well. Best regards, Daniel -- 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
