netdev - Re: [PATCH] [net][bna] Separate handling of irq type flags variable from the irq_flags request

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Message-Id: <20110715.080938.2283275421111060023.davem@davemloft.net>
Date:	Fri, 15 Jul 2011 08:09:38 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	shyam.iyer.t@...il.com
Cc:	netdev@...r.kernel.org, rmody@...cade.com, ddutt@...cade.com,
	huangj@...cade.com, ivecera@...hat.com, shyam_iyer@...l.com
Subject: Re: [PATCH] [net][bna] Separate handling of irq type flags
 variable from the irq_flags request_irq variable

From: Shyam Iyer <shyam.iyer.t@...il.com>
Date: Thu, 14 Jul 2011 21:00:32 -0400

> Commit 5f77898de17ff983ff0e2988b73a6bdf4b6f9f8b does not completely fix the problem of handling allocations with irqs disabled..
> The below patch on top of it fixes the problem completely.
> 
> Based on review by "Ivan Vecera" <ivecera@...hat.com>..
> "
> Small note, the root of the problem was that non-atomic allocation was requested with IRQs disabled. Your patch description does not contain wwhy 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.
> "
> 
> Signed-off-by: Shyam Iyer <shyam_iyer@...l.com>

Applied.
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