linux-kernel - USB HCD: avoid duplicate local_irq

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Message-Id: <200710230328.33915.arnd@arndb.de>
Date:	Tue, 23 Oct 2007 03:28:31 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	gregkh@...e.de
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>, matthew@....cx,
	ralf@...ux-mips.org, adobriyan@...il.com, viro@....linux.org.uk,
	viro@...iv.linux.org.uk, LKML <linux-kernel@...r.kernel.org>,
	linux-arch@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-usb-devel@...ts.sourceforge.net
Subject: USB HCD: avoid duplicate local_irq_disable()

usb_hcd_flush_endpoint() has a retry loop that starts with a spin_lock_irq(),
but only gives up the spinlock, not the irq_disable before jumping to the
rescan label.

Split the spin_lock_irq into the retryable part and the local_irq_disable()
that is only done once as a micro-optimization and slight cleanup.

Signed-off-by: Arnd Bergmann <arnd@...db.de>

---

On Tuesday 23 October 2007, I wrote:
> I tried the trivial annotation below and (with lockdep enabled) got a few
> warnings at boot time, but only one that I could still find in the log
> buffer:

One more such example that was not found by lockdep. I guess this counts
as a false positive, as it is clearly harmless, but working around
it is a small optimization for the case where local_irq_disable()
is a hypervisor call.

Should we try to fix this class of (non-)problem in other places?
Will this patch cause a different warning with lockdep since now we
are pairing spin_lock() with spin_unlock_irq()?

--- a/drivers/usb/core/hcd.c
+++ b/drivers/usb/core/hcd.c
@@ -1312,8 +1312,9 @@ void usb_hcd_flush_endpoint(struct usb_device *udev,
 	hcd = bus_to_hcd(udev->bus);

 	/* No more submits can occur */
+	local_irq_disable();
 rescan:
-	spin_lock_irq(&hcd_urb_list_lock);
+	spin_lock(&hcd_urb_list_lock);
 	list_for_each_entry (urb, &ep->urb_list, urb_list) {
 		int	is_in;

-
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