linux-kernel - Re: [PATCH] clocksource: Do not drop unheld reference on device node

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Date:	Fri, 22 Nov 2013 17:31:46 +0100
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Thierry Reding <thierry.reding@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>
CC:	Arnd Bergmann <arnd@...db.de>,
	Rob Herring <rob.herring@...xeda.com>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	David Brown <davidb@...eaurora.org>
Subject: Re: [PATCH] clocksource: Do not drop unheld reference on device node

On 11/22/2013 05:16 PM, Thierry Reding wrote:
> On Sat, Oct 19, 2013 at 12:49:48AM +0200, Thierry Reding wrote:
>> When booting a recent kernel on ARM with OF_DYNAMIC enabled, the kernel
>> warns about the following:
>>
>> 	[    0.000000] ERROR: Bad of_node_put() on /timer@...04600
>> 	[    0.000000] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.12.0-rc5-next-20131017-00077-gedfd827-dirty #406
>> 	[    0.000000] [<c0015b68>] (unwind_backtrace+0x0/0xf4) from [<c00117e4>] (show_stack+0x10/0x14)
>> 	[    0.000000] [<c00117e4>] (show_stack+0x10/0x14) from [<c055f734>] (dump_stack+0x9c/0xc8)
>> 	[    0.000000] [<c055f734>] (dump_stack+0x9c/0xc8) from [<c03b47d4>] (of_node_release+0x90/0x9c)
>> 	[    0.000000] [<c03b47d4>] (of_node_release+0x90/0x9c) from [<c03b5084>] (of_find_matching_node_and_match+0x78/0xb4)
>> 	[    0.000000] [<c03b5084>] (of_find_matching_node_and_match+0x78/0xb4) from [<c07887c8>] (clocksource_of_init+0x60/0x70)
>> 	[    0.000000] [<c07887c8>] (clocksource_of_init+0x60/0x70) from [<c076e99c>] (start_kernel+0x1f4/0x33c)
>> 	[    0.000000] [<c076e99c>] (start_kernel+0x1f4/0x33c) from [<80008074>] (0x80008074)
>>
>> This is caused by clocksource_of_init() dropping a reference on the
>> device node that it never took. The reference taken by the loop is
>> implicitly dropped on subsequent iterations. See the implementation of
>> and the comment on top of the of_find_matching_node_and_match()
>> function for reference (no pun intended).
>>
>> Signed-off-by: Thierry Reding <treding@...dia.com>
>> ---
>>   drivers/clocksource/clksrc-of.c | 1 -
>>   1 file changed, 1 deletion(-)
>
> Can someone look at this?

Yes. Sounds like I missed it.

This regression has been introduced by:

commit 326e31eebe61dc838e031ea16968b2cfb43443e3
Author: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Date:   Tue Oct 1 11:00:53 2013 +0200

     clocksource: Put nodes passed to CLOCKSOURCE_OF_DECLARE callbacks 
centrally

     Instead of letting each driver call of_node_put do it centrally in the
     loop that also calls the CLOCKSOURCE_OF_DECLARE callbacks. This is less
     prone to error and also moves getting and putting the references 
into the
     same function.

     Consequently all respective of_node_put calls in drivers are removed.

     Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
     Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
     Acked-by: David Brown <davidb@...eaurora.org>


>> diff --git a/drivers/clocksource/clksrc-of.c b/drivers/clocksource/clksrc-of.c
>> index 35639cf4..b9ddd9e 100644
>> --- a/drivers/clocksource/clksrc-of.c
>> +++ b/drivers/clocksource/clksrc-of.c
>> @@ -35,6 +35,5 @@ void __init clocksource_of_init(void)
>>
>>   		init_func = match->data;
>>   		init_func(np);
>> -		of_node_put(np);
>>   	}
>>   }
>> --
>> 1.8.4
>>


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