On Fri, 8 Mar 2013, Oliver Neukum wrote: > On Friday 08 March 2013 12:55:08 Alan Stern wrote: > > On Sat, 9 Mar 2013, Alexey Khoroshilov wrote: > > > > > As it was described by Oliver Neukum in commit acbe2fe > > > "USB: Don't use GFP_KERNEL while we cannot reset a storage device": > > > > > > Memory allocations with GFP_KERNEL can cause IO to a storage device > > > which can fail resulting in a need to reset the device. Therefore > > > GFP_KERNEL cannot be safely used between usb_lock_device() > > > and usb_unlock_device(). Replace by GFP_NOIO. > > > > > > The patch fixes the same issue in usb/core/devio.c. > > > All the allocations fixed are under usb_lock_device() from usbdev_do_ioctl(). > > > > > > Found by Linux Driver Verification project (linuxtesting.org). > > > > I don't know if this is a good idea. People can and do submit > > transfers requiring a lot of buffer space. Switching to GFP_NOIO > > will make those allocations a lot more likely to fail. > > > > Oliver, what do you think? > > Ideally we'd split memory allocation and use, by it fixes a bug. > Better allocation failure than deadlock. In fact we wouldn't deadlock. This is because usb_lock_device_for_reset() gives up if it can't obtain the device lock after one second of trying. We'd just end up with a failure to reset, leading to an I/O failure. Probably the mass-storage device would be taken off-line... but there wouldn't be a deadlock. Under the circumstances, I'd say that the consequences of merging this patch would be worse than the consequences of keeping things as they are now. 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
