usb-storage: implement "soft" unbinding

This patch (as1092) implements "soft" unbinding for usb-storage.  When
the disconnect routine is called, all commands and reset delays are
allowed to complete normally until after scsi_remove_host() returns.
This means that the commands needed for an orderly shutdown will be
sent through to the device.

Unlike before, the driver will now execute every command that it
accepts.  Hence there's no need for special code to catch unexecuted
commands and fail them.

The new sequence of events when disconnect runs goes as follows:

	If the device is truly unplugged, set the DISCONNECTING
	flag so we won't try to access it any more.

	If the SCSI-scanning thread hasn't started up yet, prevent
	it from doing anything by setting the new DONT_SCAN flag.
	Then wake it up and wait for it to terminate.

	Remove the SCSI host.  This unbinds the upper-level drivers,
	doing an orderly shutdown.  Commands sent to quiesce the
	device will be transmitted normally, unless the device is
	unplugged.

	Set the DISCONNECTING flag so that we won't accept any new
	commands that might get submitted (there aren't supposed to be
	any) and we won't try to access the device for resets.

	Tell the control thread to exit by waking it up with no
	pending command, and wait for it to terminate.

	Go on to do all the other normal stuff: releasing resources,
	freeing memory, and so on.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 36 insertions, 41 deletions

diff --git a/drivers/usb/storage/usb.c b/drivers/usb/storage/usb.c
index 6b14f8d253f1..6bfd99dd57aa 100644
--- a/drivers/usb/storage/usb.c
+++ b/drivers/usb/storage/usb.c
@@ -320,16 +320,17 @@ static int usb_stor_control_thread(void * __us)
 		/* lock the device pointers */
 		mutex_lock(&(us->dev_mutex));
 
-		/* if the device has disconnected, we are free to exit */
-		if (test_bit(US_FLIDX_DISCONNECTING, &us->dflags)) {
-			US_DEBUGP("-- exiting\n");
+		/* lock access to the state */
+		scsi_lock(host);
+
+		/* When we are called with no command pending, we're done */
+		if (us->srb == NULL) {
+			scsi_unlock(host);
 			mutex_unlock(&us->dev_mutex);
+			US_DEBUGP("-- exiting\n");
 			break;
 		}
 
-		/* lock access to the state */
-		scsi_lock(host);
-
 		/* has the command timed out *already* ? */
 		if (test_bit(US_FLIDX_TIMED_OUT, &us->dflags)) {
 			us->srb->result = DID_ABORT << 16;
@@ -384,12 +385,8 @@ static int usb_stor_control_thread(void * __us)
 		/* lock access to the state */
 		scsi_lock(host);
 
-		/* did the command already complete because of a disconnect? */
-		if (!us->srb)
-			;		/* nothing to do */
-
 		/* indicate that the command is done */
-		else if (us->srb->result != DID_ABORT << 16) {
+		if (us->srb->result != DID_ABORT << 16) {
 			US_DEBUGP("scsi cmd done, result=0x%x\n", 
 				   us->srb->result);
 			us->srb->scsi_done(us->srb);
@@ -820,11 +817,10 @@ static void usb_stor_release_resources(struct us_data *us)
 	US_DEBUGP("-- %s\n", __func__);
 
 	/* Tell the control thread to exit.  The SCSI host must
-	 * already have been removed so it won't try to queue
-	 * any more commands.
+	 * already have been removed and the DISCONNECTING flag set
+	 * so that we won't accept any more commands.
 	 */
 	US_DEBUGP("-- sending exit command to thread\n");
-	set_bit(US_FLIDX_DISCONNECTING, &us->dflags);
 	complete(&us->cmnd_ready);
 	if (us->ctl_thread)
 		kthread_stop(us->ctl_thread);
@@ -859,39 +855,36 @@ static void dissociate_dev(struct us_data *us)
 	usb_set_intfdata(us->pusb_intf, NULL);
 }
 
-/* First stage of disconnect processing: stop all commands and remove
- * the host */
+/* First stage of disconnect processing: stop SCSI scanning,
+ * remove the host, and stop accepting new commands
+ */
 static void quiesce_and_remove_host(struct us_data *us)
 {
 	struct Scsi_Host *host = us_to_host(us);
 
-	/* Prevent new USB transfers, stop the current command, and
-	 * interrupt a SCSI-scan or device-reset delay */
-	scsi_lock(host);
-	set_bit(US_FLIDX_DISCONNECTING, &us->dflags);
-	scsi_unlock(host);
-	usb_stor_stop_transport(us);
-	wake_up(&us->delay_wait);
+	/* If the device is really gone, cut short reset delays */
+	if (us->pusb_dev->state == USB_STATE_NOTATTACHED)
+		set_bit(US_FLIDX_DISCONNECTING, &us->dflags);
 
-	/* queuecommand won't accept any new commands and the control
-	 * thread won't execute a previously-queued command.  If there
-	 * is such a command pending, complete it with an error. */
-	mutex_lock(&us->dev_mutex);
-	if (us->srb) {
-		us->srb->result = DID_NO_CONNECT << 16;
-		scsi_lock(host);
-		us->srb->scsi_done(us->srb);
-		us->srb = NULL;
-		complete(&us->notify);		/* in case of an abort */
-		scsi_unlock(host);
-	}
-	mutex_unlock(&us->dev_mutex);
+	/* Prevent SCSI-scanning (if it hasn't started yet)
+	 * and wait for the SCSI-scanning thread to stop.
+	 */
+	set_bit(US_FLIDX_DONT_SCAN, &us->dflags);
+	wake_up(&us->delay_wait);
+	wait_for_completion(&us->scanning_done);
 
-	/* Now we own no commands so it's safe to remove the SCSI host */
+	/* Removing the host will perform an orderly shutdown: caches
+	 * synchronized, disks spun down, etc.
+	 */
 	scsi_remove_host(host);
 
-	/* Wait for the SCSI-scanning thread to stop */
-	wait_for_completion(&us->scanning_done);
+	/* Prevent any new commands from being accepted and cut short
+	 * reset delays.
+	 */
+	scsi_lock(host);
+	set_bit(US_FLIDX_DISCONNECTING, &us->dflags);
+	scsi_unlock(host);
+	wake_up(&us->delay_wait);
 }
 
 /* Second stage of disconnect processing: deallocate all resources */
@@ -919,12 +912,12 @@ static int usb_stor_scan_thread(void * __us)
 		printk(KERN_DEBUG "usb-storage: waiting for device "
 				"to settle before scanning\n");
 		wait_event_freezable_timeout(us->delay_wait,
-				test_bit(US_FLIDX_DISCONNECTING, &us->dflags),
+				test_bit(US_FLIDX_DONT_SCAN, &us->dflags),
 				delay_use * HZ);
 	}
 
 	/* If the device is still connected, perform the scanning */
-	if (!test_bit(US_FLIDX_DISCONNECTING, &us->dflags)) {
+	if (!test_bit(US_FLIDX_DONT_SCAN, &us->dflags)) {
 
 		/* For bulk-only devices, determine the max LUN value */
 		if (us->protocol == US_PR_BULK &&
@@ -1023,6 +1016,7 @@ static int storage_probe(struct usb_interface *intf,
 	if (IS_ERR(th)) {
 		printk(KERN_WARNING USB_STORAGE 
 		       "Unable to start the device-scanning thread\n");
+		complete(&us->scanning_done);
 		quiesce_and_remove_host(us);
 		result = PTR_ERR(th);
 		goto BadDevice;
@@ -1065,6 +1059,7 @@ static struct usb_driver usb_storage_driver = {
 	.pre_reset =	storage_pre_reset,
 	.post_reset =	storage_post_reset,
 	.id_table =	storage_usb_ids,
+	.soft_unbind =	1,
 };
 
 static int __init usb_stor_init(void)