Re: [PATCH] usb: check for signals in chaoskey read function

From: Keith Packard
Date: Wed Feb 17 2016 - 13:06:57 EST

Oliver Neukum <oneukum@xxxxxxxx> writes:

> On Tue, 2016-02-16 at 11:09 -0800, Keith Packard wrote:
>> I could be convinced that the driver should be using a different path
>> through the USB stack that would allow a signal to wake up while
>> waiting
>> for the URB to complete, but this patch at least avoids needing to
>> wait
>> for a huge read to finish. The other option would be to eliminate the
>> loop reading multiple URBs from the device, but that would reduce the
>> available bandwidth from the device pretty considerably.
>
> Do these do the job?

Yup, with a few minor fixes to pass the right arguments:

diff --git a/drivers/usb/misc/chaoskey.c b/drivers/usb/misc/chaoskey.c
index 67102b4..76350e4 100644
--- a/drivers/usb/misc/chaoskey.c
+++ b/drivers/usb/misc/chaoskey.c
@@ -156,14 +156,14 @@ static int chaoskey_probe(struct usb_interface *interface,
if (dev->buf == NULL)
goto out;

- dev->urb = usb_alloc_urb(GFP_KERNEL, 0);
+ dev->urb = usb_alloc_urb(0, GFP_KERNEL);

if (!dev->urb)
goto out;

usb_fill_bulk_urb(dev->urb,
udev,
- usb_rcvbulkpipe(udev, altsetting->endpoint[in_ep].desc.bEndpointAddress),
+ usb_rcvbulkpipe(udev, in_ep),
dev->buf,
size,
chaos_read_callback,

The first patch also has the URB allocation, which should be in the
second patch. I removed the comment about 'more bandwidth' as the driver
is still synchronous and runs at the same speed as before.

Thanks very much for making this 'right', instead of just kludging it.

Here's a fixed sequence:

From 6676d98364b10db5e30816dd6f9305439ee8e658 Mon Sep 17 00:00:00 2001
From: Oliver Neukum <oneukum@xxxxxxxx>
Date: Wed, 17 Feb 2016 09:58:11 -0800
Subject: [PATCH 1/2] usb/misc/chaoskey: Cleanup probe failure paths

Shares the cleanup code between all probe failure paths, instead of
having per-failure cleanup at each point in the function.

Signed-off-by: Oliver Neukum <oneukum@xxxxxxxx>
Signed-off-by: Keith Packard <keithp@xxxxxxxxxx>
---
drivers/usb/misc/chaoskey.c | 37 +++++++++++++++++++------------------
1 file changed, 19 insertions(+), 18 deletions(-)

diff --git a/drivers/usb/misc/chaoskey.c b/drivers/usb/misc/chaoskey.c
index 23c7948..cb7b829 100644
--- a/drivers/usb/misc/chaoskey.c
+++ b/drivers/usb/misc/chaoskey.c
@@ -93,10 +93,13 @@ struct chaoskey {

static void chaoskey_free(struct chaoskey *dev)
{
- usb_dbg(dev->interface, "free");
- kfree(dev->name);
- kfree(dev->buf);
- kfree(dev);
+ if (dev) {
+ usb_dbg(dev->interface, "free");
+ usb_free_urb(dev->urb);
+ kfree(dev->name);
+ kfree(dev->buf);
+ kfree(dev);
+ }
}

static int chaoskey_probe(struct usb_interface *interface,
@@ -107,7 +110,7 @@ static int chaoskey_probe(struct usb_interface *interface,
int i;
int in_ep = -1;
struct chaoskey *dev;
- int result;
+ int result = -ENOMEM;
int size;

usb_dbg(interface, "probe %s-%s", udev->product, udev->serial);
@@ -142,14 +145,12 @@ static int chaoskey_probe(struct usb_interface *interface,
dev = kzalloc(sizeof(struct chaoskey), GFP_KERNEL);

if (dev == NULL)
- return -ENOMEM;
+ goto out;

dev->buf = kmalloc(size, GFP_KERNEL);

- if (dev->buf == NULL) {
- kfree(dev);
- return -ENOMEM;
- }
+ if (dev->buf == NULL)
+ goto out;

/* Construct a name using the product and serial values. Each
* device needs a unique name for the hwrng code
@@ -158,11 +159,8 @@ static int chaoskey_probe(struct usb_interface *interface,
if (udev->product && udev->serial) {
dev->name = kmalloc(strlen(udev->product) + 1 +
strlen(udev->serial) + 1, GFP_KERNEL);
- if (dev->name == NULL) {
- kfree(dev->buf);
- kfree(dev);
- return -ENOMEM;
- }
+ if (dev->name == NULL)
+ goto out;

strcpy(dev->name, udev->product);
strcat(dev->name, "-");
@@ -186,9 +184,7 @@ static int chaoskey_probe(struct usb_interface *interface,
result = usb_register_dev(interface, &chaoskey_class);
if (result) {
usb_err(interface, "Unable to allocate minor number.");
- usb_set_intfdata(interface, NULL);
- chaoskey_free(dev);
- return result;
+ goto out;
}

dev->hwrng.name = dev->name ? dev->name : chaoskey_driver.name;
@@ -215,6 +211,11 @@ static int chaoskey_probe(struct usb_interface *interface,

usb_dbg(interface, "chaoskey probe success, size %d", dev->size);
return 0;
+
+out:
+ usb_set_intfdata(interface, NULL);
+ chaoskey_free(dev);
+ return result;
}

static void chaoskey_disconnect(struct usb_interface *interface)
--
2.7.0

From 01d91276c9dd8183ef524d45da3e0a3438fc133a Mon Sep 17 00:00:00 2001
From: Oliver Neukum <oneukum@xxxxxxxx>
Date: Wed, 17 Feb 2016 10:01:33 -0800
Subject: [PATCH 2/2] usb/misc/chaoskey: introduce an URB for asynchronous
reads

To allow for and clean handling of signals an URB is introduced.

Signed-off-by: Oliver Neukum <oneukum@xxxxxxxx>
Signed-off-by: Keith Packard <keithp@xxxxxxxxxx>
---
drivers/usb/misc/chaoskey.c | 85 ++++++++++++++++++++++++++++++++++-----------
1 file changed, 64 insertions(+), 21 deletions(-)

diff --git a/drivers/usb/misc/chaoskey.c b/drivers/usb/misc/chaoskey.c
index cb7b829..76350e4 100644
--- a/drivers/usb/misc/chaoskey.c
+++ b/drivers/usb/misc/chaoskey.c
@@ -73,6 +73,8 @@ static const struct usb_device_id chaoskey_table[] = {
};
MODULE_DEVICE_TABLE(usb, chaoskey_table);

+static void chaos_read_callback(struct urb *urb);
+
/* Driver-local specific stuff */
struct chaoskey {
struct usb_interface *interface;
@@ -80,7 +82,8 @@ struct chaoskey {
struct mutex lock;
struct mutex rng_lock;
int open; /* open count */
- int present; /* device not disconnected */
+ bool present; /* device not disconnected */
+ bool reading; /* ongoing IO */
int size; /* size of buf */
int valid; /* bytes of buf read */
int used; /* bytes of buf consumed */
@@ -88,6 +91,7 @@ struct chaoskey {
struct hwrng hwrng; /* Embedded struct for hwrng */
int hwrng_registered; /* registered with hwrng API */
wait_queue_head_t wait_q; /* for timeouts */
+ struct urb *urb; /* for performing IO */
char *buf;
};

@@ -152,6 +156,19 @@ static int chaoskey_probe(struct usb_interface *interface,
if (dev->buf == NULL)
goto out;

+ dev->urb = usb_alloc_urb(0, GFP_KERNEL);
+
+ if (!dev->urb)
+ goto out;
+
+ usb_fill_bulk_urb(dev->urb,
+ udev,
+ usb_rcvbulkpipe(udev, in_ep),
+ dev->buf,
+ size,
+ chaos_read_callback,
+ dev);
+
/* Construct a name using the product and serial values. Each
* device needs a unique name for the hwrng code
*/
@@ -238,6 +255,7 @@ static void chaoskey_disconnect(struct usb_interface *interface)
mutex_lock(&dev->lock);

dev->present = 0;
+ usb_poison_urb(dev->urb);

if (!dev->open) {
mutex_unlock(&dev->lock);
@@ -312,14 +330,33 @@ static int chaoskey_release(struct inode *inode, struct file *file)
return 0;
}

+static void chaos_read_callback(struct urb *urb)
+{
+ struct chaoskey *dev = urb->context;
+ int status = urb->status;
+
+ usb_dbg(dev->interface, "callback status (%d)", status);
+
+ if (status == 0)
+ dev->valid = urb->actual_length;
+ else
+ dev->valid = 0;
+
+ dev->used = 0;
+
+ /* must be seen first before validity is announced */
+ smp_wmb();
+
+ dev->reading = false;
+ wake_up(&dev->wait_q);
+}
+
/* Fill the buffer. Called with dev->lock held
*/
static int _chaoskey_fill(struct chaoskey *dev)
{
DEFINE_WAIT(wait);
int result;
- int this_read;
- struct usb_device *udev = interface_to_usbdev(dev->interface);

usb_dbg(dev->interface, "fill");

@@ -344,21 +381,31 @@ static int _chaoskey_fill(struct chaoskey *dev)
return result;
}

- result = usb_bulk_msg(udev,
- usb_rcvbulkpipe(udev, dev->in_ep),
- dev->buf, dev->size, &this_read,
- NAK_TIMEOUT);
+ dev->reading = true;
+ result = usb_submit_urb(dev->urb, GFP_KERNEL);
+ if (result < 0) {
+ result = usb_translate_errors(result);
+ dev->reading = false;
+ goto out;
+ }
+
+ result = wait_event_interruptible_timeout(
+ dev->wait_q,
+ !dev->reading,
+ NAK_TIMEOUT);

+ if (result < 0)
+ goto out;
+
+ if (result == 0)
+ result = -ETIMEDOUT;
+ else
+ result = dev->valid;
+out:
/* Let the device go back to sleep eventually */
usb_autopm_put_interface(dev->interface);

- if (result == 0) {
- dev->valid = this_read;
- dev->used = 0;
- }
-
- usb_dbg(dev->interface, "bulk_msg result %d this_read %d",
- result, this_read);
+ usb_dbg(dev->interface, "read %d bytes", dev->valid);

return result;
}
@@ -396,13 +443,7 @@ static ssize_t chaoskey_read(struct file *file,
goto bail;
if (dev->valid == dev->used) {
result = _chaoskey_fill(dev);
- if (result) {
- mutex_unlock(&dev->lock);
- goto bail;
- }
-
- /* Read returned zero bytes */
- if (dev->used == dev->valid) {
+ if (result < 0) {
mutex_unlock(&dev->lock);
goto bail;
}
@@ -436,6 +477,8 @@ bail:
return read_count;
}
usb_dbg(dev->interface, "empty read, result %d", result);
+ if (result == -ETIMEDOUT)
+ result = -EAGAIN;
return result;
}

--
2.7.0


--
-keith

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