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SubjectRe: [PATCH] clocksource: Do not drop unheld reference on device node
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.)

Best regards
Uwe

--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | http://www.pengutronix.de/ |
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