netdev - RE: [PATCH] [v3][net][bna] Fix call trace when interrupts are disabled while sleeping function kzalloc is called

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Date:	Tue, 12 Jul 2011 14:42:36 +0200
From:	Ivan Vecera <ivecera@...hat.com>
To:	Shyam_Iyer@...l.com
Cc:	shyam.iyer.t@...il.com, netdev@...r.kernel.org, rmody@...cade.com,
	ddutt@...cade.com, huangj@...cade.com, davem@...emloft.net
Subject: RE: [PATCH] [v3][net][bna] Fix call trace when interrupts are
 disabled while sleeping function kzalloc is called

On Fri, 2011-07-08 at 03:23 +0530, Shyam_Iyer@...l.com wrote:
> 
> > -----Original Message-----
> > From: Ivan Vecera [mailto:ivecera@...hat.com]
> > Sent: Thursday, July 07, 2011 11:14 AM
> > To: Shyam Iyer
> > Cc: netdev@...r.kernel.org; rmody@...cade.com; ddutt@...cade.com;
> > huangj@...cade.com; davem@...emloft.net; Iyer, Shyam
> > Subject: Re: [PATCH] [v3][net][bna] Fix call trace when interrupts are
> > disabled while sleeping function kzalloc is called
> > 
> > Small note, the root of the problem was that non-atomic allocation was
> > requested with IRQs disabled. Your patch description does not contain
> > why were the IRQs disabled.
> > The function bnad_mbox_irq_alloc incorrectly uses 'flags' var for two
> > different things, 1) to save current CPU flags and 2) for request_irq
> > call.
> > First the spin_lock_irqsave disables the IRQs and saves _all_ CPU flags
> > (including one that enables/disables interrupts) to 'flags'. Then the
> > 'flags' is overwritten by 0 or 0x80 (IRQF_SHARED). Finally the
> > spin_unlock_irqrestore should restore saved flags, but these flags are
> > now either 0x00 or 0x80. The interrupt bit value in flags register on
> > x86 arch is 0x100.
> > This means that the interrupt bit is zero (IRQs disabled) after
> > spin_unlock_irqrestore so the request_irq function is called with
> > disabled interrupts.
> 
> That seems to make a lot more sense.. and that way I don't have to initialize the flags variable outside of the spin_lock_irqsave/restore bracket to preserve the irqs not being disabled when allocating in request_irq
> 
> Would the below patch make sense instead...? (Note that since davem has accepted the earlier one this is on top of the already committed patch)
> 
Yes, this is much cleaner...

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