On Thu, 26 Nov 2015, Steinar H. Gunderson wrote:
> On Wed, Nov 25, 2015 at 10:29:53AM -0500, Alan Stern wrote:
> > I want to see a modified version of your patch. Several things need to
> > be changed or fixed, but the major change needs to be the way memory is
> > allocated. It should be done as part of the mmap system call, not as a
> > separate ioctl.
>
> I took a stab at this. The attached patch doesn't fix any of your other
> issues, but could you take a look at whether the mmap part looks sane?
> I've verified that it works in practice with my own code, and see no
> performance regressions. It is still the case that you can't mix mmap
> and non-mmap transfers on the same device; I suppose that should be governed
> by a zerocopy flag instead of “are there any mmap-ed areas”.
As I recall, Markus's original patch took care of this by checking to
see whether the transfer buffer was in one of the mmap'ed areas. If it
was then the transfer would be zerocopy; otherwise it would be normal.
That seems like a reasonable approach.
> Let me go through your other issues:
>
> > There are numerous smaller issues: The allocated memory needs to be
> > charged against usbfs_memory_usage
>
> I'll fix this.
>
> > the memory should be allocated using dma_zalloc_coherent instead of
> > kmalloc,
>
> dma_zalloc_coherent returns a dma_handle in addition to the memory itself;
> should we just throw this away?
No, the handle has to be stored for use when an URB is submitted and
when the memory is deallocated -- it is a required argument for
dma_free_coherent().
> > proc_do_submiturb should
> > check that the buffer starts anywhere within the allocated memory
> > rather than just at the beginning
>
> I'll fix this, too.
>
> > , and so on.
>
> Clarification appreciated ;-)
Detailed notes below.
> diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
> index 38ae877c..9a1a7d6 100644
> --- a/drivers/usb/core/devio.c
> +++ b/drivers/usb/core/devio.c
> @@ -69,6 +69,7 @@ struct usb_dev_state {
> spinlock_t lock; /* protects the async urb lists */
> struct list_head async_pending;
> struct list_head async_completed;
> + struct list_head memory_list;
> wait_queue_head_t wait; /* wake up if a request completed */
> unsigned int discsignr;
> struct pid *disc_pid;
> @@ -96,6 +97,17 @@ struct async {
> u8 bulk_status;
> };
>
> +struct usb_memory {
> + struct list_head memlist;
> + int vma_use_count;
> + int usb_use_count;
> + u32 offset;
What's the reason for the "offset" member? It doesn't seem to do
anything.
> + u32 size;
> + void *mem;
You'll need to store the DMA address as well.
> + unsigned long vm_start;
> + struct usb_dev_state *ps;
> +};
> +
> static bool usbfs_snoop;
> module_param(usbfs_snoop, bool, S_IRUGO | S_IWUSR);
> MODULE_PARM_DESC(usbfs_snoop, "true to log all usbfs traffic");
> @@ -157,6 +169,74 @@ static int connected(struct usb_dev_state *ps)
> ps->dev->state != USB_STATE_NOTATTACHED);
> }
>
> +static struct usb_memory *
> +alloc_usb_memory(struct usb_dev_state *ps, size_t size)
> +{
> + struct usb_memory *usbm;
> + void *mem;
> + unsigned long flags;
> +
> + mem = alloc_pages_exact(size, GFP_KERNEL | GFP_DMA32);
dma_zalloc_coherent(), not alloc_pages_exact().
> + if (!mem)
> + return NULL;
> +
> + usbm = kzalloc(sizeof(struct usb_memory), GFP_KERNEL);
> + if (!usbm) {
> + free_pages_exact(mem, size);
> + return NULL;
> + }
> + memset(mem, 0x0, PAGE_SIZE << get_order(size));
Then this line won't be needed.
> + usbm->mem = mem;
> + usbm->offset = virt_to_phys(mem);
> + usbm->size = size;
> + usbm->ps = ps;
> + spin_lock_irqsave(&ps->lock, flags);
> + list_add_tail(&usbm->memlist, &ps->memory_list);
> + spin_unlock_irqrestore(&ps->lock, flags);
> +
> + return usbm;
> +}
This subroutine should be merged into usbdev_mmap().
In fact, all the memory-oriented routines should be located together
in the source file. It's confusing to put some of them near the start
and others near the end.
> +
> +static void dec_use_count(struct usb_memory *usbm, int *count)
> +{
> + struct usb_dev_state *ps = usbm->ps;
> + unsigned long flags;
> +
> + spin_lock_irqsave(&ps->lock, flags);
> + WARN_ON(count != &usbm->usb_use_count && count != &usbm->vma_use_count);
> + --*count;
> + if (usbm->usb_use_count == 0 && usbm->vma_use_count == 0) {
Forget about the WARN_ON; you know all the callers because this patch
introduces them. If you prefer, instead of a pointer pass an
enumeration value: USB_MEMORY_URB_COUNT or USB_MEMORY_VMA_COUNT.
Also, you might change the name to make it a little less generic. For
example, dec_usb_memory_use_count().
> + list_del_init(&usbm->memlist);
> + free_pages_exact(usbm->mem, usbm->size);
> + usbfs_decrease_memory_usage(
> + usbm->size + sizeof(struct usb_memory));
> + kfree(usbm);
> + }
> + spin_unlock_irqrestore(&ps->lock, flags);
> +}
> +
> +static struct usb_memory *
> +find_memory_area(struct usb_dev_state *ps, const struct usbdevfs_urb *uurb)
> +{
> + struct usb_memory *usbm = NULL, *iter;
> + unsigned long flags;
> + unsigned long uurb_start = (unsigned long)uurb->buffer;
> +
> + spin_lock_irqsave(&ps->lock, flags);
> + list_for_each_entry(iter, &ps->memory_list, memlist) {
> + if (iter->usb_use_count == 0 &&
I don't think this is necessary. It should be legal to keep the data
for two URBs in the same memory region, so long as they don't overlap.
> + uurb_start >= iter->vm_start &&
> + uurb->buffer_length <= iter->vm_start - uurb_start +
> + (PAGE_SIZE << get_order(iter->size))) {
Shouldn't this be:
uurb->start >= iter->vm_start &&
uurb->start < iter->vm_start + iter->size &&
uurb->buffer_length <= iter->vm_start + iter->size -
uurb->start) {
> + usbm = iter;
> + usbm->usb_use_count++;
> + break;
> + }
> + }
> + spin_unlock_irqrestore(&ps->lock, flags);
> + return usbm;
> +}
> +
> static loff_t usbdev_lseek(struct file *file, loff_t offset, int orig)
> {
> loff_t ret;
> @@ -288,6 +368,9 @@ static struct async *alloc_async(unsigned int
> numisoframes)
>
> static void free_async(struct async *as)
> {
> + struct usb_memory *usbm = NULL, *usbm_iter;
> + unsigned long flags;
> + struct usb_dev_state *ps = as->ps;
> int i;
>
> put_pid(as->pid);
> @@ -297,8 +380,22 @@ static void free_async(struct async *as)
> if (sg_page(&as->urb->sg[i]))
> kfree(sg_virt(&as->urb->sg[i]));
> }
> +
> + spin_lock_irqsave(&ps->lock, flags);
> + list_for_each_entry(usbm_iter, &ps->memory_list, memlist) {
> + if (usbm_iter->mem == as->urb->transfer_buffer) {
> + usbm = usbm_iter;
> + break;
> + }
> + }
> + spin_unlock_irqrestore(&ps->lock, flags);
There's no need to do this. Just store the usbm pointer in the as
structure.
> +
> kfree(as->urb->sg);
> - kfree(as->urb->transfer_buffer);
> + if (usbm == NULL)
> + kfree(as->urb->transfer_buffer);
> + else
> + dec_use_count(usbm, &usbm->usb_use_count);
> +
> kfree(as->urb->setup_packet);
> usb_free_urb(as->urb);
> usbfs_decrease_memory_usage(as->mem_usage);
> @@ -910,6 +1007,7 @@ static int usbdev_open(struct inode *inode, struct file
> *file)
> INIT_LIST_HEAD(&ps->list);
> INIT_LIST_HEAD(&ps->async_pending);
> INIT_LIST_HEAD(&ps->async_completed);
> + INIT_LIST_HEAD(&ps->memory_list);
> init_waitqueue_head(&ps->wait);
> ps->discsignr = 0;
> ps->disc_pid = get_pid(task_pid(current));
> @@ -938,6 +1036,8 @@ static int usbdev_release(struct inode *inode, struct
> file *file)
> struct usb_dev_state *ps = file->private_data;
> struct usb_device *dev = ps->dev;
> unsigned int ifnum;
> + struct list_head *p, *q;
> + struct usb_memory *tmp;
> struct async *as;
>
> usb_lock_device(dev);
> @@ -962,6 +1062,14 @@ static int usbdev_release(struct inode *inode, struct
> file *file)
> free_async(as);
> as = async_getcompleted(ps);
> }
> +
> + list_for_each_safe(p, q, &ps->memory_list) {
> + tmp = list_entry(p, struct usb_memory, memlist);
> + list_del(p);
> + if (tmp->mem)
> + free_pages_exact(tmp->mem, tmp->size);
> + kfree(tmp);
No, you can't do this here. The memory might still be in use by the
VMA. You have to do:
list_del(&ps->memory_list);
perhaps with a comment explaining when the usb_memory structures and
the memory buffers get freed (i.e., when the use counters go to 0).
> + }
> kfree(ps);
> return 0;
> }
> @@ -1291,6 +1399,7 @@ static int proc_do_submiturb(struct usb_dev_state *ps,
> struct usbdevfs_urb *uurb
> struct usb_host_endpoint *ep;
> struct async *as = NULL;
> struct usb_ctrlrequest *dr = NULL;
> + struct usb_memory *usbm = NULL;
> unsigned int u, totlen, isofrmlen;
> int i, ret, is_in, num_sgs = 0, ifnum = -1;
> int number_of_packets = 0;
> @@ -1372,9 +1481,17 @@ static int proc_do_submiturb(struct usb_dev_state *ps,
> struct usbdevfs_urb *uurb
> uurb->type = USBDEVFS_URB_TYPE_INTERRUPT;
> goto interrupt_urb;
> }
> - num_sgs = DIV_ROUND_UP(uurb->buffer_length, USB_SG_SIZE);
> - if (num_sgs == 1 || num_sgs > ps->dev->bus->sg_tablesize)
> - num_sgs = 0;
> + /* do not use SG buffers when memory mapped segments
> + * are allocated
> + */
> + if (list_empty(&ps->memory_list)) {
No, first call find_memory_area(). If the result is NULL then do this.
> + num_sgs = DIV_ROUND_UP(uurb->buffer_length,
> + USB_SG_SIZE);
> + if (num_sgs == 1 ||
> + num_sgs > ps->dev->bus->sg_tablesize) {
> + num_sgs = 0;
> + }
> + }
> if (ep->streams)
> stream_id = uurb->stream_id;
> break;
> @@ -1439,6 +1556,8 @@ static int proc_do_submiturb(struct usb_dev_state *ps,
> struct usbdevfs_urb *uurb
> goto error;
> }
>
> + as->ps = ps;
> +
Why move this? Isn't it fine where it is?
> u += sizeof(struct async) + sizeof(struct urb) + uurb->buffer_length +
> num_sgs * sizeof(struct scatterlist);
> ret = usbfs_increase_memory_usage(u);
> @@ -1476,21 +1595,32 @@ static int proc_do_submiturb(struct usb_dev_state
> *ps, struct usbdevfs_urb *uurb
> totlen -= u;
> }
> } else if (uurb->buffer_length > 0) {
> - as->urb->transfer_buffer = kmalloc(uurb->buffer_length,
> - GFP_KERNEL);
> + if (!list_empty(&ps->memory_list)) {
> + usbm = find_memory_area(ps, uurb);
> + if (usbm) {
> + as->urb->transfer_buffer = usbm->mem;
> + } else {
> + ret = -ENOMEM;
> + goto error;
> + }
> + } else {
> + as->urb->transfer_buffer = kmalloc(uurb->buffer_length,
> + GFP_KERNEL);
> + }
> if (!as->urb->transfer_buffer) {
> ret = -ENOMEM;
> goto error;
> }
>
> - if (!is_in) {
> + if (!is_in && usbm == NULL) {
> if (copy_from_user(as->urb->transfer_buffer,
> uurb->buffer,
> uurb->buffer_length)) {
> ret = -EFAULT;
> goto error;
> }
> - } else if (uurb->type == USBDEVFS_URB_TYPE_ISO) {
> + } else if (uurb->type == USBDEVFS_URB_TYPE_ISO &&
> + usbm == NULL) {
> /*
> * Isochronous input data may end up being
> * discontiguous if some of the packets are short.
> @@ -1543,9 +1673,8 @@ static int proc_do_submiturb(struct usb_dev_state *ps,
> struct usbdevfs_urb *uurb
> }
> kfree(isopkt);
> isopkt = NULL;
> - as->ps = ps;
> as->userurb = arg;
> - if (is_in && uurb->buffer_length > 0)
> + if (is_in && uurb->buffer_length > 0 && usbm == NULL)
I think you should keep this even when usbm is not NULL. No?
> as->userbuffer = uurb->buffer;
> else
> as->userbuffer = NULL;
When you use dma_zalloc_coherent(), you have to tell the USB core that
the buffer is already mapped for DMA by setting the URB_NO_TRANSFER_DMA_MAP
flag in urb->transfer_flags and by storing the DMA address in
urb->transfer_dma.
> @@ -1604,6 +1733,8 @@ static int proc_do_submiturb(struct usb_dev_state *ps,
> struct usbdevfs_urb *uurb
> return 0;
>
> error:
> + if (usbm)
> + dec_use_count(usbm, &usbm->usb_use_count);
> kfree(isopkt);
> kfree(dr);
> if (as)
You have to change processcompl(). The copy_urb_data() call isn't
needed when zerocopy is being used -- in fact, it rather defeats the
purpose of zerocopy!
> @@ -2337,6 +2468,57 @@ static long usbdev_ioctl(struct file *file, unsigned
> int cmd,
> return ret;
> }
>
> +static void usbdev_vm_open(struct vm_area_struct *vma)
> +{
> + struct usb_memory *usbm = vma->vm_private_data;
> + unsigned long flags;
> +
> + spin_lock_irqsave(&usbm->ps->lock, flags);
> + ++usbm->vma_use_count;
> + spin_unlock_irqrestore(&usbm->ps->lock, flags);
> +}
> +
> +static void usbdev_vm_close(struct vm_area_struct *vma)
> +{
> + struct usb_memory *usbm = vma->vm_private_data;
> +
> + dec_use_count(usbm, &usbm->vma_use_count);
> +}
> +
> +struct vm_operations_struct usbdev_vm_ops = {
> + .open = usbdev_vm_open,
> + .close = usbdev_vm_close
> +};
> +
> +static int usbdev_mmap(struct file *file, struct vm_area_struct *vma)
> +{
> + struct usb_memory *usbm = NULL;
> + struct usb_dev_state *ps = file->private_data;
> + size_t size = vma->vm_end - vma->vm_start;
> + int ret;
> +
> + ret = usbfs_increase_memory_usage(size + sizeof(struct usb_memory));
> + if (ret)
> + return ret;
> +
> + usbm = alloc_usb_memory(ps, size);
> + if (!usbm)
> + return -ENOMEM;
> +
> + if (remap_pfn_range(vma, vma->vm_start,
> + virt_to_phys(usbm->mem) >> PAGE_SHIFT,
> + size, vma->vm_page_prot) < 0)
> + return -EAGAIN;
As Oliver pointed out, the memory needs to be reclaimed and accounted
for on the failure pathways.
> +
> + usbm->vm_start = vma->vm_start;
> + vma->vm_flags |= VM_IO;
> + vma->vm_flags |= (VM_DONTEXPAND | VM_DONTDUMP);
> + vma->vm_ops = &usbdev_vm_ops;
> + vma->vm_private_data = usbm;
> + usbdev_vm_open(vma);
> + return 0;
> +}
> +
> #ifdef CONFIG_COMPAT
> static long usbdev_compat_ioctl(struct file *file, unsigned int cmd,
> unsigned long arg)
> @@ -2373,6 +2555,7 @@ const struct file_operations usbdev_file_operations = {
> #ifdef CONFIG_COMPAT
> .compat_ioctl = usbdev_compat_ioctl,
> #endif
> + .mmap = usbdev_mmap,
> .open = usbdev_open,
> .release = usbdev_release,
> };
Alan Stern
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