netdev - [PATCH v2] usb/core: remove "always" from usb_unlink

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Message-ID: <20120229220432.GD11628@linutronix.de>
Date:	Wed, 29 Feb 2012 23:04:32 +0100
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Oliver Neukum <oliver@...kum.org>, netdev@...r.kernel.org,
	linux-usb@...r.kernel.org, Alan Stern <stern@...land.harvard.edu>
Subject: [PATCH v2] usb/core: remove "always" from usb_unlink_urb() kernel
 doc entry

The kernel doc entry for usb_unlink_urb() contains the phrase "This
request is always asynchronous.". The "always" leads to the assumption
that the ->complete() callback is not called from within
usb_unlink_urb(). This is not true. The HCD is allowed to call the
->complete() from within ->urb_dequeue() if it is appropriate for the
hardware.
This patch updates the kernel doc so usb-device driver authors make sure
to drop all locks (and make sure it is okay to drop them) which are
acquired by the complete callback before calling usb_unlink_urb().

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
v1..v2:
 - add Alan's suggestion
 - s/hcd/HCD

 drivers/usb/core/urb.c |   11 +++++++----
 1 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/core/urb.c b/drivers/usb/core/urb.c
index f4f20c7..7239a73 100644
--- a/drivers/usb/core/urb.c
+++ b/drivers/usb/core/urb.c
@@ -527,10 +527,13 @@ EXPORT_SYMBOL_GPL(usb_submit_urb);
  * a driver's I/O routines to insure that all URB-related activity has
  * completed before it returns.
  *
- * This request is always asynchronous.  Success is indicated by
- * returning -EINPROGRESS, at which time the URB will probably not yet
- * have been given back to the device driver.  When it is eventually
- * called, the completion function will see @urb->status == -ECONNRESET.
+ * This request is asynchronous, however the HCD might call the ->complete()
+ * callback during unlink. Therefore when drivers call usb_unlink_urb(), they
+ * must not hold any locks that may be taken by the completion function.
+ * Success is indicated by returning -EINPROGRESS, at which time the URB will
+ * probably not yet have been given back to the device driver. When it is
+ * eventually called, the completion function will see @urb->status ==
+ * -ECONNRESET.
  * Failure is indicated by usb_unlink_urb() returning any other value.
  * Unlinking will fail when @urb is not currently "linked" (i.e., it was
  * never submitted, or it was unlinked before, or the hardware is already
-- 
1.7.9

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