From: Daniel Lezcano <daniel.lezcano@linaro.org>
To: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Cc: Thierry Reding <thierry.reding@gmail.com>,
Thomas Gleixner <tglx@linutronix.de>,
Arnd Bergmann <arnd@arndb.de>,
Rob Herring <rob.herring@calxeda.com>,
devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
David Brown <davidb@codeaurora.org>
Subject: Re: [PATCH] clocksource: Do not drop unheld reference on device node
Date: Sun, 24 Nov 2013 22:28:15 +0100 [thread overview]
Message-ID: <52926F6F.3050104@linaro.org> (raw)
In-Reply-To: <20131122192257.GX28642@pengutronix.de>
On 11/22/2013 08:22 PM, Uwe Kleine-König wrote:
> On Fri, Nov 22, 2013 at 05:31:46PM +0100, Daniel Lezcano wrote:
>> 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@50004600
>>>> [ 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).
> I only saw the end of the comment saying:
>
> Returns a node pointer with refcount incremented, use
> of_node_put() on it when done.
>
> Maybe that could be improved to something like:
>
> /**
> * of_find_matching_node_and_match - Find a node based on an of_device_id
> * match table
> * @from: The node to start searching from or NULL, the node you pass
> * will not be searched, only the next one will; typically, you
> * pass what the previous call returned.
> * @matches: ...
> * @match: ...
> *
> * Reference counting: Puts a reference on @from and increases the
> * reference count of the returned node.
> */
>
>>>>
>>>> Signed-off-by: Thierry Reding <treding@nvidia.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@pengutronix.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@pengutronix.de>
>> Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
>> Acked-by: David Brown <davidb@codeaurora.org>
> Still all but the hook in clocksource_of_init of this commit was
> correct, right? (Well, but this buggy hunk makes the commit log wrong.)
I don't understand your comment, can you elaborate ?
Thanks
-- Daniel
--
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next prev parent reply other threads:[~2013-11-24 21:28 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-18 22:49 [PATCH] clocksource: Do not drop unheld reference on device node Thierry Reding
2013-11-22 16:16 ` Thierry Reding
2013-11-22 16:31 ` Daniel Lezcano
2013-11-22 19:22 ` Uwe Kleine-König
2013-11-24 21:28 ` Daniel Lezcano [this message]
2013-11-25 7:29 ` Uwe Kleine-König
2013-11-25 8:57 ` Daniel Lezcano
2013-11-25 9:04 ` Thierry Reding
2013-11-25 8:59 ` Thierry Reding
2013-11-28 8:23 ` Daniel Lezcano
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