linux-kernel - Re: [PATCH v10 03/19] arm: fiq: Replace default FIQ handler

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Message-ID: <20140902113655.GO30401@n2100.arm.linux.org.uk>
Date:	Tue, 2 Sep 2014 12:36:55 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Daniel Thompson <daniel.thompson@...aro.org>
Cc:	paulmck@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	kgdb-bugreport@...ts.sourceforge.net, patches@...aro.org,
	linaro-kernel@...ts.linaro.org,
	John Stultz <john.stultz@...aro.org>,
	Anton Vorontsov <anton.vorontsov@...aro.org>,
	Colin Cross <ccross@...roid.com>, kernel-team@...roid.com,
	Rob Herring <robherring2@...il.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Ben Dooks <ben.dooks@...ethink.co.uk>,
	Catalin Marinas <catalin.marinas@....com>,
	Dave Martin <Dave.Martin@....com>,
	Fabio Estevam <festevam@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Nicolas Pitre <nico@...aro.org>
Subject: Re: [PATCH v10 03/19] arm: fiq: Replace default FIQ handler

On Tue, Sep 02, 2014 at 12:03:11PM +0100, Daniel Thompson wrote:
> On 28/08/14 17:15, Paul E. McKenney wrote:
> > On Thu, Aug 28, 2014 at 04:54:25PM +0100, Daniel Thompson wrote:
> >> On 28/08/14 16:01, Russell King - ARM Linux wrote:
> >>> There's concerns with whether either printk() in check_flags() could
> >>> be reached too (flags there should always indicate that IRQs were
> >>> disabled, so that reduces down to a question about just the first
> >>> printk() there.)
> >>>
> >>> There's also the very_verbose() stuff for RCU lockdep classes which
> >>> Paul says must not be enabled.
> >>>
> >>> Lastly, Paul isn't a lockdep expert, but he sees nothing that prevents
> >>> lockdep doing the deadlock checking as a result of the above call.
> >>>
> >>> So... this coupled with my feeling that notifiers make it too easy for
> >>> unreviewed code to be hooked into this path, I'm fairly sure that we
> >>> don't want to be calling atomic notifier chains from FIQ context.
> 
> Having esablished (above) that RCU usage is safe from FIQ I have been
> working on the assumption that your feeling regarding unreviewed code
> is sufficient on its own to avoid using notifiers (and also to avoid
> a list of function pointers like on x86).

I'm assuming that "your" above refers to Paul here, since you addressed
your message To: Paul and only copied me for information purposes.

If not, please address your message more appropriately so as to avoid
confusion.

Thanks.

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