linux-kernel - Re: [linux-usb-devel] USB HCD: avoid duplicate local_irq

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Date:	Sat, 27 Oct 2007 15:14:40 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Greg KH <greg@...ah.com>
cc:	Arnd Bergmann <arnd@...db.de>, <gregkh@...e.de>,
	<linux-arch@...r.kernel.org>,
	<linux-usb-devel@...ts.sourceforge.net>, <matthew@....cx>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>, <ralf@...ux-mips.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	<viro@...iv.linux.org.uk>, <viro@....linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	<adobriyan@...il.com>
Subject: Re: [linux-usb-devel] USB HCD: avoid duplicate local_irq_disable()

On Thu, 25 Oct 2007, Greg KH wrote:

> On Tue, Oct 23, 2007 at 12:01:37AM -0400, Alan Stern wrote:
> > On Tue, 23 Oct 2007, Arnd Bergmann wrote:
> > 
> > > 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.
> > 
> > I agree with your sentiment, but it would be better to solve this 
> > problem without using local_irq_disable().  The patch below does this.
> > 
> > ---
> > 
> > Signed-off-by: Alan Stern <stern@...land.harvard.edu>
> 
> Alan, is this something you want added to the tree and in before 2.6.24
> is out?

Yes.  It's a small thing, but we're better off keeping IRQ
enable/disable calls properly balanced.

Alan Stern

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