netdev - Re: [PATCH kernel 2.6.35-rc3-git7] axnet_cs: use spin_lock_irqsave in ax

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Date:	Sun, 11 Jul 2010 04:12:34 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	David Miller <davem@...emloft.net>
Cc:	ken_kawasaki@...ing.nifty.jp, netdev@...r.kernel.org
Subject: Re: [PATCH kernel 2.6.35-rc3-git7] axnet_cs: use spin_lock_irqsave
 in ax_interrupt

On Sat, 2010-07-10 at 19:49 -0700, David Miller wrote:
> From: Ben Hutchings <bhutchings@...arflare.com>
> Date: Sun, 11 Jul 2010 03:46:28 +0100
> 
> > On Sat, 2010-07-10 at 20:18 +0900, Ken Kawasaki wrote:
> >> axnet_cs:
> >>     use spin_lock_irqsave instead of spin_lock in ax_interrupt
> > [...]
> > 
> > I assume this is because it's now called from ei_watchdog() and not only
> > from interrupt context.  Perhaps you should explain that in the commit
> > message.
> 
> No, interrupt handlers in general may not assume that interrupts
> are off or on when they are invoked.
> 
> Therefore they must use irqflags saving/restoring.

But an interrupt handler will not be called recursively for the same
IRQ.  Since this device only uses one IRQ, surely it was OK to use
spin_lock() in this function so long as it was only called from the
interrupt handler.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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