On Sun, 2016-01-24 at 13:22 -0800, Greg KH wrote: > On Thu, Jan 21, 2016 at 03:18:48PM +0100, Oliver Neukum wrote: > > Quting the relevant thread: > > > > > In fact, I suspect the locking added by the kernel 3.13 commit for > > > read_descriptors() is invalid because read_descriptors() performs no USB > > > activity; read_descriptors() just reads information from an allocated > > > memory structure. This structure is protected as the structure is > > > existing before and after the sysfs vfs descriptors entry is created or > > > destroyed. > > > > You're right. For some reason I thought that usb_deauthorize_device() > > would destroy the rawdescriptor structures (as mentioned in that > > commit's Changelog), but it doesn't. The locking in read_descriptors() > > is unnecessary. > > > > > The information is only written at the time of enumeration > > > and does not change. At least that is my understanding. > > > > > > It is noted that in our testing of kernel 3.8 on ARM, that sysfs > > > read_descriptors() was non-blocking because the kernel 3.13 comment was > > > not there. > > > > > > The pre-kernel 3.13 sysfs read_descriptors() seemed to work OK. > > > > > > Proposal: > > > ========= > > > > > > Remove the usb_lock_device(udev) and usb_unlock_device(udev) from > > > devices/usb/core/sysfs.c in read_descriptors() that was added by the > > > kernel 3.13 commit > > > "232275a USB: fix substandard locking for the sysfs files" > > > > > > Any comments to this proposal ? > > > > It seems okay to me. Please submit a patch. > > > > So this removes the locking making the point about -EINTR in > > the first path moot. > > I don't understand, should I drop this patch? Should I drop the first > patch? Hi, good question. I made patches to a) make sleeping interruptible b) remove unnecessary locking b depends on a as is. I can redo them if you wish to. Or you can take them both in the current order. Just tell me whatever is clearer in the logs. Regards Oliver -- 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
