Dear Oliver, > You cannot honor GFP_NOIO
GFP_NOIO is used in original kernel space transmission relating sk_buf. It is not used for userspace transmission. I added 'if' statement around the block to skip the block where GFP_NOIO is used for kernel space transmission. > the cleanest solution would be an additional flag to match requiring > a kernel space driver Other allocations are regular GFP_KERNEL or GFP_ATOMIC. Thank you, n.iwata // > -----Original Message----- > From: linux-usb-ow...@vger.kernel.org > [mailto:linux-usb-ow...@vger.kernel.org] On Behalf Of Oliver Neukum > Sent: Sunday, January 03, 2016 2:07 AM > To: fx IWATA NOBUO > Cc: valentina.mane...@gmail.com; shuah...@samsung.com; > gre...@linuxfoundation.org; linux-usb@vger.kernel.org; fx MICHIMURA > TADAO; Alan Stern > Subject: Re: [PATCH v5 04/11] usbip: kernel module for userspace URBs > transmission > > On Wed, 2015-12-30 at 15:10 +0900, Nobuo Iwata wrote: > > Originally, USB/IP transmits requests and response PDUs for > > preparation to transfer URBs in user space, after the preparation, > > URBs are transmitted in kernel space. > > > > To make easy to introduce application network protocols like WebSocket > > and so on, the driver, usbip_ux.ko, forwards URBs to USB/IP user space > > utilities. It's just like fuse driver for user space file system. > > Then, utilities transfer URBs in user space. > > Hi, > > this raises fundamental questions. Just like fuse you are importing > limitations this way. Fuse cannot do shared writable memory mappings because > the VM can deadlock if you drop the GFP_NOFS requirement. That is inevitable > if you go to user space, as user space is paged memory. Putting a HCD into > user space the problem becomes even worse. You cannot honor GFP_NOIO. > That means that essentially no block device can run without the risk of > a deadlock. > > It seems to me that the cleanest solution would be an additional flag to > match requiring a kernel space driver would be the cleanest solution. > > Regards > Oliver > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-usb" in > the body of a message to majord...@vger.kernel.org More majordomo info at > http://vger.kernel.org/majordomo-info.html
