patch "usb: devio, do not warn when allocation fails" added to usb-linus

This is a note to let you know that I've just added the patch titled

usb: devio, do not warn when allocation fails

to my usb git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git
in the usb-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From: Jiri Slaby <[email protected]>
Date: Wed, 15 Jun 2016 15:56:11 +0200
Subject: usb: devio, do not warn when allocation fails

usbdev_mmap allocates a buffer. The size of the buffer is determined by a user. So with this code (no need to be root):

	int fd = open("/dev/bus/usb/001/001", O_RDONLY);
	mmap(NULL, 0x800000, PROT_READ, MAP_SHARED, fd, 0);

we can see a warning:

WARNING: CPU: 0 PID: 21771 at ../mm/page_alloc.c:3563 __alloc_pages_slowpath+0x1036/0x16e0()
...
Call Trace:
 [<ffffffff8117a3ae>] ? warn_slowpath_null+0x2e/0x40
 [<ffffffff815178b6>] ? __alloc_pages_slowpath+0x1036/0x16e0
 [<ffffffff81516880>] ? warn_alloc_failed+0x250/0x250
 [<ffffffff8151226b>] ? get_page_from_freelist+0x75b/0x28b0
 [<ffffffff815184e3>] ? __alloc_pages_nodemask+0x583/0x6b0
 [<ffffffff81517f60>] ? __alloc_pages_slowpath+0x16e0/0x16e0
 [<ffffffff810565d4>] ? dma_generic_alloc_coherent+0x104/0x220
 [<ffffffffa0269e56>] ? hcd_buffer_alloc+0x1d6/0x3e0 [usbcore]
 [<ffffffffa0269c80>] ? hcd_buffer_destroy+0xa0/0xa0 [usbcore]
 [<ffffffffa0228f05>] ? usb_alloc_coherent+0x65/0x90 [usbcore]
 [<ffffffffa0275c05>] ? usbdev_mmap+0x1a5/0x770 [usbcore]

...

Allocations like this one should be marked as __GFP_NOWARN. So do so.

The size could be also clipped by something like:

	if (size >= (1 << (MAX_ORDER + PAGE_SHIFT - 1)))
		return -ENOMEM;

But I think the overall limit of 16M (by usbfs_increase_memory_usage) is enough, so that we only silence the warning here.

---
 drivers/usb/core/devio.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

index e9f5043a2167..472cbcdf7456 100644
@@ -241,7 +241,8 @@ static int usbdev_mmap(struct file *file, struct vm_area_struct *vma)
 		goto error_decrease_mem;
 	}
 
-	mem = usb_alloc_coherent(ps->dev, size, GFP_USER, &dma_handle);
+	mem = usb_alloc_coherent(ps->dev, size, GFP_USER | __GFP_NOWARN,
+			&dma_handle);
 	if (!mem) {
 		ret = -ENOMEM;
 		goto error_free_usbm;

2.9.2