Re: [PATCH v1 2/2] of: Let of_for_each_phandle fallback to non-negative cell_count

From: Peter Rosin <peda@axentia.se>
To: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
	"Geert Uytterhoeven" <geert@linux-m68k.org>
Cc: Rob Herring <robh@kernel.org>,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
	<devicetree@vger.kernel.org>,
	Frank Rowand <frowand.list@gmail.com>,
	Joerg Roedel <joro@8bytes.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux-Renesas <linux-renesas-soc@vger.kernel.org>,
	Wolfram Sang <wsa+renesas@sang-engineering.com>,
	Linux IOMMU <iommu@lists.linux-foundation.org>,
	"linux-mediatek@lists.infradead.org"
	<linux-mediatek@lists.infradead.org>,
	Linux I2C <linux-i2c@vger.kernel.org>,
	Sascha Hauer <kernel@pengutronix.de>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	Will Deacon <will@kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Robin Murphy <robin.murphy@arm.com>
Subject: Re: [PATCH v1 2/2] of: Let of_for_each_phandle fallback to non-negative cell_count
Date: Tue, 17 Sep 2019 11:25:46 +0000	[thread overview]
Message-ID: <489c90fb-a135-4fd8-ecb9-46404bd3c234@axentia.se> (raw)
In-Reply-To: <20190917101303.t5otztdus7y3ayau@pengutronix.de>

On 2019-09-17 12:13, Uwe Kleine-König wrote:
> Hello Geert,
> 
> On Tue, Sep 17, 2019 at 11:40:25AM +0200, Geert Uytterhoeven wrote:
>> Hi Rob, Uwe,
>>
>> On Fri, Sep 13, 2019 at 11:58 PM Rob Herring <robh@kernel.org> wrote:
>>> On Sat, 24 Aug 2019 15:28:46 +0200, =?UTF-8?q?Uwe=20Kleine-K=C3=B6nig?=          wrote:
>>>> Referencing device tree nodes from a property allows to pass arguments.
>>>> This is for example used for referencing gpios. This looks as follows:
>>>>
>>>>       gpio_ctrl: gpio-controller {
>>>>               #gpio-cells = <2>
>>>>               ...
>>>>       }
>>>>
>>>>       someothernode {
>>>>               gpios = <&gpio_ctrl 5 0 &gpio_ctrl 3 0>;
>>>>               ...
>>>>       }
>>>>
>>>> To know the number of arguments this must be either fixed, or the
>>>> referenced node is checked for a $cells_name (here: "#gpio-cells")
>>>> property and with this information the start of the second reference can
>>>> be determined.
>>>>
>>>> Currently regulators are referenced with no additional arguments. To
>>>> allow some optional arguments without having to change all referenced
>>>> nodes this change introduces a way to specify a default cell_count. So
>>>> when a phandle is parsed we check for the $cells_name property and use
>>>> it as before if present. If it is not present we fall back to
>>>> cells_count if non-negative and only fail if cells_count is smaller than
>>>> zero.
>>>>
>>>> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
>>
>> This is now commit e42ee61017f58cd9 ("of: Let of_for_each_phandle fallback
>> to non-negative cell_count") in robh/for-next, which causes a lock-up when
>> booting a shmobile_defconfig kernel on r8a7791/koelsch:
>>
>> rcu: INFO: rcu_sched self-detected stall on CPU
>> rcu:     0-....: (2099 ticks this GP) idle=6fe/1/0x40000002
>> softirq=29/29 fqs=1050
>>  (t=2100 jiffies g=-1131 q=0)
>> NMI backtrace for cpu 0
>> CPU: 0 PID: 1 Comm: swapper/0 Not tainted
>> 5.3.0-rc2-shmobile-00050-ge42ee61017f58cd9 #376
>> Hardware name: Generic R-Car Gen2 (Flattened Device Tree)
>> [<c010f8ac>] (unwind_backtrace) from [<c010b620>] (show_stack+0x10/0x14)
>> [<c010b620>] (show_stack) from [<c073d038>] (dump_stack+0x7c/0x9c)
>> [<c073d038>] (dump_stack) from [<c0742e80>] (nmi_cpu_backtrace+0xa0/0xb8)
>> [<c0742e80>] (nmi_cpu_backtrace) from [<c0742f1c>] (nmi_trigger_cpumask_backtrace+0x84/0x114)
>> [<c0742f1c>] (nmi_trigger_cpumask_backtrace) from [<c017d684>] (rcu_dump_cpu_stacks+0xac/0xc8)
>> [<c017d684>] (rcu_dump_cpu_stacks) from [<c017a598>] (rcu_sched_clock_irq+0x2ac/0x6b4)
>> [<c017a598>] (rcu_sched_clock_irq) from [<c0183980>] (update_process_times+0x30/0x5c)
>> [<c0183980>] (update_process_times) from [<c01941a8>] (tick_nohz_handler+0xcc/0x120)
>> [<c01941a8>] (tick_nohz_handler) from [<c05b1d40>] (arch_timer_handler_virt+0x28/0x30)
>> [<c05b1d40>] (arch_timer_handler_virt) from [<c016c9e0>] (handle_percpu_devid_irq+0xe8/0x21c)
>> [<c016c9e0>] (handle_percpu_devid_irq) from [<c0167a8c>] (generic_handle_irq+0x18/0x28)
>> [<c0167a8c>] (generic_handle_irq) from [<c0167b3c>] (__handle_domain_irq+0xa0/0xb4)
>> [<c0167b3c>] (__handle_domain_irq) from [<c03673ec>] (gic_handle_irq+0x58/0x90)
>> [<c03673ec>] (gic_handle_irq) from [<c0101a8c>] (__irq_svc+0x6c/0x90)
>> Exception stack(0xeb08dd30 to 0xeb08dd78)
>> dd20:                                     c0cc7514 20000013 00000005 00003b27
>> dd40: eb7c4020 c0cc750c 00000051 00000051 20000013 c0c66b08 eb1cdc00 00000018
>> dd60: 00000000 eb08dd80 c05c1a38 c0756c00 20000013 ffffffff
>> [<c0101a8c>] (__irq_svc) from [<c0756c00>] (_raw_spin_unlock_irqrestore+0x1c/0x20)
>> [<c0756c00>] (_raw_spin_unlock_irqrestore) from [<c05c1a38>] (of_find_node_by_phandle+0xcc/0xf0)
>> [<c05c1a38>] (of_find_node_by_phandle) from [<c05c1bb8>] (of_phandle_iterator_next+0x68/0x178)
>> [<c05c1bb8>] (of_phandle_iterator_next) from [<c05c22bc>] (of_count_phandle_with_args+0x5c/0x7c)
>> [<c05c22bc>] (of_count_phandle_with_args) from [<c053fc38>] (i2c_demux_pinctrl_probe+0x24/0x1fc)
>> [<c053fc38>] (i2c_demux_pinctrl_probe) from [<c04463c4>] (platform_drv_probe+0x48/0x94)
>> [<c04463c4>] (platform_drv_probe) from [<c0444a20>] (really_probe+0x1f0/0x2b8)
>> [<c0444a20>] (really_probe) from [<c0444e68>] (driver_probe_device+0x140/0x158)
>> [<c0444e68>] (driver_probe_device) from [<c0444ff0>] (device_driver_attach+0x44/0x5c)
>> [<c0444ff0>] (device_driver_attach) from [<c04450b4>] (__driver_attach+0xac/0xb4)
>> [<c04450b4>] (__driver_attach) from [<c0443178>] (bus_for_each_dev+0x64/0xa0)
>> [<c0443178>] (bus_for_each_dev) from [<c04438a8>] (bus_add_driver+0x148/0x1a8)
>> [<c04438a8>] (bus_add_driver) from [<c0445ad0>] (driver_register+0xac/0xf0)
>> [<c0445ad0>] (driver_register) from [<c0b010b0>] (do_one_initcall+0xa8/0x1d4)
>> [<c0b010b0>] (do_one_initcall) from [<c0b01448>] (kernel_init_freeable+0x26c/0x2c8)
>> [<c0b01448>] (kernel_init_freeable) from [<c0751c70>] (kernel_init+0x8/0x10c)
>> [<c0751c70>] (kernel_init) from [<c01010e8>] (ret_from_fork+0x14/0x2c)
>> Exception stack(0xeb08dfb0 to 0xeb08dff8)
>> dfa0:                                     00000000 00000000 00000000 00000000
>> dfc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
>> dfe0: 00000000 00000000 00000000 00000000 00000013 00000000
>>
>> Presumably it loops forever, due to a conversion of -1 to unsigned
>> somewhere?
> 
> Hmm, I fail to see the culprit. i2c_demux_pinctrl_probe calls
> of_count_phandle_with_args with cells_name=NULL. With that I don't see
> how my patch changes anything as the only change is in an if
> (it->cells_name) block that shouldn't be relevant in your case.
> 
> Can you please verify that the loop in of_count_phandle_with_args is
> indeed not terminating, e.g. with

The below indicated else-branch was not touched by e42ee61017f58cd9,
which ends up setting the count to -1 (aka 0xff...ff in this case).
No?

int of_phandle_iterator_next(struct of_phandle_iterator *it)
{

	...

		if (it->cells_name) {

			...

		} else {
			count = it->cell_count;    /* <---- SUSPECT!!! */
		}

		...
	}

	...
}

Cheers,
Peter
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