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Date: Wed, 17 Mar 2010 10:08:58 +0100
From: Johan Hovold <jhovold@...il.com>
To: Jason Wessel <jason.wessel@...driver.com>
Cc: gregkh@...e.de, Alan Stern <stern@...land.harvard.edu>,
linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
Alan Cox <alan@...ux.intel.com>,
Oliver Neukum <oliver@...kum.org>
Subject: Re: [PATCH 4/5] usb-hcd,usb-console: poll hcd device to force usb
console writes
Hi,
On Tue, Mar 16, 2010 at 04:05:45PM -0500, Jason Wessel wrote:
> This patch tries to solve the problem that data is lost because there
> are too many outstanding transmit urb's while trying to execute
> printk's to a console. The same is true if you try something like
> "echo t > /proc/sysrq-trigger".
>
> This patch takes the route of forcibly polling the hcd device to drain
> the urb queue in order to initiate the bulk write call backs. This
> only happens if the device is a usb serial console device that sets
> the max_in_flight_urbs to a non zero value in the serial device
> structure.
Why do you need to use max_in_flight_urbs for this? Shouldn't any usb
serial device be able to use the polling mode?
Currently the parameter is only used by usb_debug to limit the number of
outstanding urbs for the generic multi-urb write implementation. But now
you're adding a second meaning to the variable and use it as a flag
when you set it to -1 for pl2303 (which uses a fifo-implementation) or
URB_UPPER_LIMIT for ftdi_sio (you could simply have used -1 here as
well). If there are drivers that definitely should not use the polling
mode, it seems to me a new flag such as console_poll (or
no_console_poll) would be more appropriate.
That is, either always poll if a console or if necessary poll only if
serial->type->console_poll is set (or no_console_poll isn't).
There are a few more comments below.
> A few millisecond penalty will get incurred to allow the hcd controller
> to complete a write urb, else the console data is thrown away.
>
> The max_in_flight_urbs was reduced in the usb_debug driver because it
> is highly desired to push things out to the console in a timely
> fashion and there is no need to have a queue that large for the
> interrupt driven mode of operation when used through the tty
> interface.
>
> CC: Greg Kroah-Hartman <gregkh@...e.de>
> CC: Alan Cox <alan@...ux.intel.com>
> CC: Alan Stern <stern@...land.harvard.edu>
> CC: Oliver Neukum <oliver@...kum.org>
> CC: linux-usb@...r.kernel.org
> Signed-off-by: Jason Wessel <jason.wessel@...driver.com>
> ---
> drivers/usb/core/hcd.c | 10 +++++++++
> drivers/usb/serial/console.c | 42 +++++++++++++++++++++++++--------------
> drivers/usb/serial/ftdi_sio.c | 7 +++--
> drivers/usb/serial/pl2303.c | 6 +++-
> drivers/usb/serial/usb_debug.c | 2 +-
> include/linux/usb.h | 3 ++
> 6 files changed, 49 insertions(+), 21 deletions(-)
>
> diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
> index 2f8cedd..dd710d7 100644
> --- a/drivers/usb/core/hcd.c
> +++ b/drivers/usb/core/hcd.c
> @@ -2271,6 +2271,16 @@ usb_hcd_platform_shutdown(struct platform_device* dev)
> }
> EXPORT_SYMBOL_GPL(usb_hcd_platform_shutdown);
>
> +void
> +usb_poll_irq(struct usb_device *udev)
> +{
> + struct usb_hcd *hcd;
> +
> + hcd = bus_to_hcd(udev->bus);
> + usb_hcd_irq(0, hcd);
> +}
> +EXPORT_SYMBOL_GPL(usb_poll_irq);
> +
> /*-------------------------------------------------------------------------*/
>
> #if defined(CONFIG_USB_MON) || defined(CONFIG_USB_MON_MODULE)
> diff --git a/drivers/usb/serial/console.c b/drivers/usb/serial/console.c
> index 1ee6b2a..b6b96ff 100644
> --- a/drivers/usb/serial/console.c
> +++ b/drivers/usb/serial/console.c
> @@ -197,13 +197,37 @@ static int usb_console_setup(struct console *co, char *options)
> return retval;
> }
>
> +static void usb_do_console_write(struct usb_serial *serial,
> + struct usb_serial_port *port,
> + const char *buf, unsigned count)
> +{
> + int retval;
> + int loops = 100;
> +try_again:
> + /* pass on to the driver specific version of this function if
> + it is available */
> + if (serial->type->write)
> + retval = serial->type->write(NULL, port, buf, count);
> + else
> + retval = usb_serial_generic_write(NULL, port, buf, count);
> + if (retval < count && retval >= 0 &&
> + serial->type->max_in_flight_urbs != 0 && loops--) {
> + /* poll the hcd device because the queue is full */
> + count -= retval;
> + buf += retval;
> + udelay(100);
> + usb_poll_irq(serial->dev);
> + goto try_again;
> + }
> + dbg("%s - return value : %d", __func__, retval);
> +}
> +
> static void usb_console_write(struct console *co,
> const char *buf, unsigned count)
> {
> static struct usbcons_info *info = &usbcons_info;
> struct usb_serial_port *port = info->port;
> struct usb_serial *serial;
> - int retval = -ENODEV;
>
> if (!port || port->serial->dev->state == USB_STATE_NOTATTACHED)
> return;
> @@ -230,23 +254,11 @@ static void usb_console_write(struct console *co,
> break;
> }
> }
> - /* pass on to the driver specific version of this function if
> - it is available */
> - if (serial->type->write)
> - retval = serial->type->write(NULL, port, buf, i);
> - else
> - retval = usb_serial_generic_write(NULL, port, buf, i);
> - dbg("%s - return value : %d", __func__, retval);
> + usb_do_console_write(serial, port, buf, i);
> if (lf) {
> /* append CR after LF */
> unsigned char cr = 13;
> - if (serial->type->write)
> - retval = serial->type->write(NULL,
> - port, &cr, 1);
> - else
> - retval = usb_serial_generic_write(NULL,
> - port, &cr, 1);
> - dbg("%s - return value : %d", __func__, retval);
> + usb_do_console_write(serial, port, &cr, 1);
> }
> buf += i;
> count -= i;
> diff --git a/drivers/usb/serial/ftdi_sio.c b/drivers/usb/serial/ftdi_sio.c
> index 95ec748..c7f559c 100644
> --- a/drivers/usb/serial/ftdi_sio.c
> +++ b/drivers/usb/serial/ftdi_sio.c
> @@ -53,6 +53,9 @@
> #define DRIVER_AUTHOR "Greg Kroah-Hartman <greg@...ah.com>, Bill Ryder <bryder@....com>, Kuba Ober <kuba@...eimbrium.org>, Andreas Mohr"
> #define DRIVER_DESC "USB FTDI Serial Converters Driver"
>
> +/* number of outstanding urbs to prevent userspace DoS from happening */
> +#define URB_UPPER_LIMIT 42
> +
> static int debug;
> static __u16 vendor = FTDI_VID;
> static __u16 product;
> @@ -838,6 +841,7 @@ static struct usb_serial_driver ftdi_sio_device = {
> .ioctl = ftdi_ioctl,
> .set_termios = ftdi_set_termios,
> .break_ctl = ftdi_break_ctl,
> + .max_in_flight_urbs = URB_UPPER_LIMIT,
Here max_in_flight_urbs is simply used as a flag (could have used -1
here as well).
> };
>
>
> @@ -848,9 +852,6 @@ static struct usb_serial_driver ftdi_sio_device = {
> #define HIGH 1
> #define LOW 0
>
> -/* number of outstanding urbs to prevent userspace DoS from happening */
> -#define URB_UPPER_LIMIT 42
> -
> /*
> * ***************************************************************************
> * Utility functions
> diff --git a/drivers/usb/serial/pl2303.c b/drivers/usb/serial/pl2303.c
> index 1891cfb..2615fe1 100644
> --- a/drivers/usb/serial/pl2303.c
> +++ b/drivers/usb/serial/pl2303.c
> @@ -453,8 +453,9 @@ static void pl2303_send(struct usb_serial_port *port)
> port->write_urb->transfer_buffer_length = count;
> result = usb_submit_urb(port->write_urb, GFP_ATOMIC);
> if (result) {
> - dev_err(&port->dev, "%s - failed submitting write urb,"
> - " error %d\n", __func__, result);
> + if (!(port->port.console))
> + dev_err(&port->dev, "%s - failed submitting write urb,"
> + " error %d\n", __func__, result);
Why do you treat pl2303 different from all other drivers (including
ftdi_sio and usb_debug) which all report error when submitting an urb
failed? Is this crucial to not get locked up in some recursion?
> priv->write_urb_in_use = 0;
> /* TODO: reschedule pl2303_send */
> }
> @@ -1185,6 +1186,7 @@ static struct usb_serial_driver pl2303_device = {
> .chars_in_buffer = pl2303_chars_in_buffer,
> .attach = pl2303_startup,
> .release = pl2303_release,
> + .max_in_flight_urbs = -1,
> };
Here max_in_flight_urbs is again used as a flag in a way that is
unrelated to its original meaning as pl2303 does not uses the generic
multi-urb writes but rather a custom fifo and a single urb.
> static int __init pl2303_init(void)
> diff --git a/drivers/usb/serial/usb_debug.c b/drivers/usb/serial/usb_debug.c
> index 252cc2d..4a04552 100644
> --- a/drivers/usb/serial/usb_debug.c
> +++ b/drivers/usb/serial/usb_debug.c
> @@ -15,7 +15,7 @@
> #include <linux/usb.h>
> #include <linux/usb/serial.h>
>
> -#define URB_DEBUG_MAX_IN_FLIGHT_URBS 4000
> +#define URB_DEBUG_MAX_IN_FLIGHT_URBS 42
> #define USB_DEBUG_MAX_PACKET_SIZE 8
> #define USB_DEBUG_BRK_SIZE 8
> static char USB_DEBUG_BRK[USB_DEBUG_BRK_SIZE] = {
> diff --git a/include/linux/usb.h b/include/linux/usb.h
> index 8c9f053..a7d6cf7 100644
> --- a/include/linux/usb.h
> +++ b/include/linux/usb.h
> @@ -569,6 +569,9 @@ static inline void usb_mark_last_busy(struct usb_device *udev)
>
> /*-------------------------------------------------------------------------*/
>
> +/* for polling the hcd device */
> +extern void usb_poll_irq(struct usb_device *udev);
> +
> /* for drivers using iso endpoints */
> extern int usb_get_current_frame_number(struct usb_device *usb_dev);
Regards,
Johan
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