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USB documentation: explain lifetime rules for unlinking URBs

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This patch (as1534c) updates the documentation for usb_unlink_urb and
related functions.  It explains that the caller must prevent the URB
being unlinked from getting deallocated while the unlink is taking
place.

Signed-off-by: Alan Stern <[email protected]>
CC: Ming Lei <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
This commit is contained in:
Alan Stern 2012-03-28 16:13:28 -04:00 • committed by Greg Kroah-Hartman
commit da8bfb090c
2 changed files with 34 additions and 0 deletions
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12
drivers/usb/core/urb.c
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@ -539,6 +539,10 @@ EXPORT_SYMBOL_GPL(usb_submit_urb);
* never submitted, or it was unlinked before, or the hardware is already
* finished with it), even if the completion handler has not yet run.
*
* The URB must not be deallocated while this routine is running. In
* particular, when a driver calls this routine, it must insure that the
* completion handler cannot deallocate the URB.
*
* Unlinking and Endpoint Queues:
*
* [The behaviors and guarantees described below do not apply to virtual
@ -603,6 +607,10 @@ EXPORT_SYMBOL_GPL(usb_unlink_urb);
* with error -EPERM. Thus even if the URB's completion handler always
* tries to resubmit, it will not succeed and the URB will become idle.
*
* The URB must not be deallocated while this routine is running. In
* particular, when a driver calls this routine, it must insure that the
* completion handler cannot deallocate the URB.
*
* This routine may not be used in an interrupt context (such as a bottom
* half or a completion handler), or when holding a spinlock, or in other
* situations where the caller can't schedule().
@ -640,6 +648,10 @@ EXPORT_SYMBOL_GPL(usb_kill_urb);
* with error -EPERM. Thus even if the URB's completion handler always
* tries to resubmit, it will not succeed and the URB will become idle.
*
* The URB must not be deallocated while this routine is running. In
* particular, when a driver calls this routine, it must insure that the
* completion handler cannot deallocate the URB.
*
* This routine may not be used in an interrupt context (such as a bottom
* half or a completion handler), or when holding a spinlock, or in other
* situations where the caller can't schedule().