linux-kernel - Re: Dangerous devm_request

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Message-id: <000c01ce10cb$fdd4a4a0$f97dede0$%han@samsung.com>
Date:	Fri, 22 Feb 2013 16:12:36 +0900
From:	Jingoo Han <jg1.han@...sung.com>
To:	'Dmitry Torokhov' <dmitry.torokhov@...il.com>
Cc:	'Linus Torvalds' <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	'Andrew Morton' <akpm@...ux-foundation.org>,
	'Jingoo Han' <jg1.han@...sung.com>
Subject: Re: Dangerous devm_request_irq() conversions

On Friday, February 22, 2013 3:54 PM, Dmitry Torokhov wrote:
> 
> Hi,
> 
> It looks like a whole slew of devm_request_irq() conversions just got
> applied to mainline and many of them are quite broken.
> 
> Consider fd5231ce336e038037b4f0190a6838bdd6e17c6d or
> c1879fe80c61f3be6f2ddb82509c2e7f92a484fe: the drivers udsed first to
> free IRQ and then unregister the corresponding device ensuring that IRQ
> handler, while it runs, has the device available. The mechanic
> conversion to devm_request_irq() reverses the order of these operations
> opening the race window where IRQ can reference device (or other
> resource) that is already gone.
> 
> It would be nice if these could be reverted and revioewed again for
> correctness.

Um, other RTC drivers already have been using devm_request_threaded_irq() or
devm_request_irq() like this, before I added these patches.

For example, 
./drivers/rtc/rtc-tegra.c
./drivers/rtc/rtc-spear.c
./drivers/rtc/rtc-s3c.c
./drivers/rtc/rtc-mxc.c
./drivers/rtc/rtc-ds1553.c
./drivers/rtc/rtc-ds1511.c
./drivers/rtc/rtc-snvs.c
./drivers/rtc/rtc-imxdi.c
./drivers/rtc/rtc-tx4939.c
./drivers/rtc/rtc-mv.c
./drivers/rtc/rtc-coh901331.c
./drivers/rtc/rtc-stk17ta8.c
./drivers/rtc/rtc-lpc32xx.c
./drivers/rtc/rtc-tps65910.c
./drivers/rtc/rtc-rc5t583.c


Also, even more, some RTC drivers calls rtc_device_unregister() first,
then calls free_irq() later.

For example,
./drivers/rtc/rtc-vr41xx.c
./drivers/rtc/rtc-da9052.c
./drivers/rtc/rtc-isl1208.c
./drivers/rtc/rtc-88pm860x.c
./drivers/rtc/rtc-tps6586x.c
./drivers/rtc/rtc-mpc5121.c
./drivers/rtc/rtc-m48t59.c


Please, don't argue revert without concrete reasons.

If these devm_request_threaded_irq() or devm_request_irq() make the problem,
devm_free_irq() will be added later.


> 
> In general any conversion to devm_request_irq() needs double and triple
> checking.
> 
> Thanks.
> 
> --
> Dmitry

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