usb: cdc-acm: drain writes on close

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>

2 files changed, 35 insertions, 5 deletions

diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index a9dd28f446d8..efc4373ededb 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -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);
diff --git a/drivers/usb/class/cdc-acm.h b/drivers/usb/class/cdc-acm.h
index 94266362ca68..1f95e7aa1b66 100644
--- a/drivers/usb/class/cdc-acm.h
+++ b/drivers/usb/class/cdc-acm.h
@@ -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) */