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usb: cdc-acm: drain writes on close

Browse source 
Add a mechanism to let the write queue drain naturally before
closing the TTY, rather than always losing that data.  There
is a timeout, so it can't wait too long.

Provide missing locking inside acm_wb_is_avail(); it matters
more now.  Note, this presumes an earlier patch was applied,
removing a call to this routine where the lock was held.

Slightly improved diagnostics on write URB completion, so we
can tell when a write URB gets killed and, if so, how much
data it wrote first ... and so that I/O path is normally
silent (and can't much change timings).

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
David Brownell 2008-08-06 18:46:10 -07:00 committed by Greg Kroah-Hartman
parent 934da4635c
commit e5fbab51b4
2 changed files with 35 additions and 5 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

39
drivers/usb/class/cdc-acm.c
View file

@ -51,6 +51,7 @@
*/
#undef DEBUG
#undef VERBOSE_DEBUG
#include <linux/kernel.h>
#include <linux/errno.h>
@ -70,6 +71,9 @@
#include "cdc-acm.h"
#define ACM_CLOSE_TIMEOUT 15 /* seconds to let writes drain */
/*
* Version Information
*/
@ -85,6 +89,12 @@ static DEFINE_MUTEX(open_mutex);
#define ACM_READY(acm) (acm && acm->dev && acm->used)
#ifdef VERBOSE_DEBUG
#define verbose 1
#else
#define verbose 0
#endif
/*
* Functions for ACM control messages.
*/
@ -136,11 +146,14 @@ static int acm_wb_alloc(struct acm *acm)
static int acm_wb_is_avail(struct acm *acm)
{
int i, n;
unsigned long flags;
n = ACM_NW;
spin_lock_irqsave(&acm->write_lock, flags);
for (i = 0; i < ACM_NW; i++) {
n -= acm->wb[i].use;
}
spin_unlock_irqrestore(&acm->write_lock, flags);
return n;
}
@ -467,22 +480,28 @@ urbs:
/* data interface wrote those outgoing bytes */
static void acm_write_bulk(struct urb *urb)
{
struct acm *acm;
struct acm_wb *wb = urb->context;
struct acm *acm = wb->instance;
dbg("Entering acm_write_bulk with status %d", urb->status);
if (verbose || urb->status
|| (urb->actual_length != urb->transfer_buffer_length))
dev_dbg(&acm->data->dev, "tx %d/%d bytes -- > %d\n",
urb->actual_length,
urb->transfer_buffer_length,
urb->status);
acm = wb->instance;
acm_write_done(acm, wb);
if (ACM_READY(acm))
schedule_work(&acm->work);
else
wake_up_interruptible(&acm->drain_wait);
}
static void acm_softint(struct work_struct *work)
{
struct acm *acm = container_of(work, struct acm, work);
dbg("Entering acm_softint.");
dev_vdbg(&acm->data->dev, "tx work\n");
if (!ACM_READY(acm))
return;
tty_wakeup(acm->tty);
@ -603,6 +622,8 @@ static void acm_tty_unregister(struct acm *acm)
kfree(acm);
}
static int acm_tty_chars_in_buffer(struct tty_struct *tty);
static void acm_tty_close(struct tty_struct *tty, struct file *filp)
{
struct acm *acm = tty->driver_data;
@ -617,6 +638,13 @@ static void acm_tty_close(struct tty_struct *tty, struct file *filp)
if (acm->dev) {
usb_autopm_get_interface(acm->control);
acm_set_control(acm, acm->ctrlout = 0);
/* try letting the last writes drain naturally */
wait_event_interruptible_timeout(acm->drain_wait,
(ACM_NW == acm_wb_is_avail(acm))
|| !acm->dev,
ACM_CLOSE_TIMEOUT * HZ);
usb_kill_urb(acm->ctrlurb);
for (i = 0; i < ACM_NW; i++)
usb_kill_urb(acm->wb[i].urb);
@ -1047,6 +1075,7 @@ skip_normal_probe:
acm->urb_task.data = (unsigned long) acm;
INIT_WORK(&acm->work, acm_softint);
INIT_WORK(&acm->waker, acm_waker);
init_waitqueue_head(&acm->drain_wait);
spin_lock_init(&acm->throttle_lock);
spin_lock_init(&acm->write_lock);
spin_lock_init(&acm->read_lock);

1
drivers/usb/class/cdc-acm.h
View file

@ -113,6 +113,7 @@ struct acm {
struct usb_cdc_line_coding line; /* bits, stop, parity */
struct work_struct work; /* work queue entry for line discipline waking up */
struct work_struct waker;
wait_queue_head_t drain_wait; /* close processing */
struct tasklet_struct urb_task; /* rx processing */
spinlock_t throttle_lock; /* synchronize throtteling and read callback */
unsigned int ctrlin; /* input control lines (DCD, DSR, RI, break, overruns) */