> It's never a NOP unless the unlink somehow completed already.
> As I said: using async unlinks because I want to see all the
> synchronization right here, clearly visible, no hidden magic.
OK, maybe I am dense, but this doesn't make sense.
Let's have another closer look:
--- 1.33/drivers/usb/core/message.c Fri Aug 1 05:03:12 2003
+++ edited/drivers/usb/core/message.c Fri Aug 8 16:39:14 2003
@@ -16,75 +16,60 @@
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/mm.h>
+#include <linux/completion.h>
#include <asm/byteorder.h>
#include "hcd.h" /* for usbcore internals */
#include "usb.h"
-struct usb_api_data {
- wait_queue_head_t wqh;
- int done;
-};
-
static void usb_api_blocking_completion(struct urb *urb, struct pt_regs *regs)
{
- struct usb_api_data *awd = (struct usb_api_data *)urb->context;
-
- awd->done = 1;
- wmb();
- wake_up(&awd->wqh);
+ complete ((struct completion *)urb->context);
Here, you get woken up.
}
// Starts urb and waits for completion or timeout
static int usb_start_wait_urb(struct urb *urb, int timeout, int* actual_length)
{
- DECLARE_WAITQUEUE(wait, current);
- struct usb_api_data awd;
+ DEFINE_WAIT(wait);
+ DECLARE_COMPLETION(done);
int status;
- init_waitqueue_head(&awd.wqh);
- awd.done = 0;
-
- set_current_state(TASK_UNINTERRUPTIBLE);
- add_wait_queue(&awd.wqh, &wait);
+ urb->transfer_flags |= URB_ASYNC_UNLINK;
+ urb->context = &done;
- urb->context = &awd;
+ might_sleep();
unnecessary, wait_for_completion() has the test
+ prepare_to_wait(&done.wait, &wait, TASK_UNINTERRUPTIBLE);
You prepare to sleep using a conventional wait queue
status = usb_submit_urb(urb, GFP_ATOMIC);
- if (status) {
- // something went wrong
- usb_free_urb(urb);
- set_current_state(TASK_RUNNING);
- remove_wait_queue(&awd.wqh, &wait);
- return status;
- }
-
- while (timeout && !awd.done)
- {
- timeout = schedule_timeout(timeout);
- set_current_state(TASK_UNINTERRUPTIBLE);
- rmb();
- }
+ if (status != 0) {
+ urb->actual_length = 0;
- set_current_state(TASK_RUNNING);
- remove_wait_queue(&awd.wqh, &wait);
+ /* normal case: we woke without a timeout */
+ } else if (schedule_timeout((timeout == 0)
And here you sleep, doing the wait on the waitqueue
of the struct completion
+ ? MAX_SCHEDULE_TIMEOUT
+ : timeout) != 0) {
+ status = urb->status;
- if (!timeout && !awd.done) {
- if (urb->status != -EINPROGRESS) { /* No callback?!! */
- printk(KERN_ERR "usb: raced timeout, "
- "pipe 0x%x status %d time left %d\n",
- urb->pipe, urb->status, timeout);
- status = urb->status;
- } else {
- warn("usb_control/bulk_msg: timeout");
- usb_unlink_urb(urb); // remove urb safely
- status = -ETIMEDOUT;
+ /* abnormal: timed out, so force completion via unlink */
+ } else {
+ status = usb_unlink_urb(urb);
+ switch (status) {
+ case -EINPROGRESS: /* normal */
+ case -EBUSY: /* already completing */
+ dev_err(&urb->dev->dev, "control/bulk timeout\n");
+ break;
+ default:
+ /* shouldn't happen */
+ dev_err(&urb->dev->dev, "c/b unlink err %d\n", status);
+ break;
}
- } else
- status = urb->status;
+ wait_for_completion(&done);
What for? You already waited with schedule_timeout.
+ /* NOTE: HCDs return this status too */
+ status = -ETIMEDOUT;
+ }
+ finish_wait(&done.wait, &wait);
if (actual_length)
*actual_length = urb->actual_length;
-
usb_free_urb(urb);
return status;
}
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