linux-kernel - Re: [PATCH v2 1/2] i2c: tegra: Better handle case where CPU0 is busy for a long time

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Message-ID: <9a3d283c-d4ff-c55a-3ebf-4e08d35792ec@gmail.com>
Date:   Mon, 27 Apr 2020 18:38:02 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Jon Hunter <jonathanh@...dia.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        Wolfram Sang <wsa@...-dreams.de>,
        Manikanta Maddireddy <mmaddireddy@...dia.com>,
        Vidya Sagar <vidyas@...dia.com>
Cc:     linux-i2c@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2 1/2] i2c: tegra: Better handle case where CPU0 is busy
 for a long time

27.04.2020 17:45, Dmitry Osipenko пишет:
> 27.04.2020 17:13, Dmitry Osipenko пишет:
>> 27.04.2020 15:46, Dmitry Osipenko пишет:
>>> 23.04.2020 13:56, Jon Hunter пишет:
>>>>>> So I think that part of the problem already existed prior to these
>>>>>> patches. Without your patches I see ...
>>>>>>
>>>>>> [   59.543528] tegra-i2c 7000d000.i2c: i2c transfer timed out
>>>>>> [   59.549036] vdd_sata,avdd_plle: failed to disable
>>>>>> [   59.553778] Failed to disable avdd-plle: -110
>>>>>> [   59.558150] tegra-pcie 3000.pcie: failed to disable regulators: -110
>>>>> Does this I2C timeout happen with my patches? Could you please post full
>>>>> logs of an older and the recent kernel versions?
>>>> I believe that it does, but I need to check.
>>>>
>>>
>>> Jon, could you please confirm that you're seeing those regulator-disable
>>> errors with my patch? I don't see those errors in yours original log [1].
>>>
>>> [1]
>>> https://lore.kernel.org/lkml/1e259e22-c300-663a-e537-18d854e0f478@nvidia.com/
>>>
>>> Again, could you please post the *full* logs?
>>>
>>> If regulator's disabling was "failing" before without my patch because
>>> of the I2C interrupt being force-disabled during of NOIRQ phase, and now
>>> regulator's disabling succeeds with my patch because IRQ is manually
>>> handled after the timeout, then this could be bad. It means that
>>> regulator was actually getting disabled, but I2C driver was timing out
>>> because interrupt couldn't be handled in NOIRQ phase, which should
>>> result in a dead PCIe on a resume from suspend since regulator's core
>>> thinks that regulator is enabled (I2C said it failed to disable), while
>>> it is actually disabled.
>>>
>>> Do you have anything plugged into the PCIe slot in yours testing farm?
>>> It wouldn't surprise me if the plugged card isn't functional after
>>> resume from suspend on a stable kernels.
>>>
>>
>> I actually now see that interrupt is not allowed to be enabled during
>> the NOIRQ phase:
>>
>> https://elixir.bootlin.com/linux/v5.7-rc3/source/kernel/irq/manage.c#L640
>>
>> it should be worthwhile to turn it into a WARN_ON.
>>
> 
> Oh, wait! There is already a warning there.. hmm.
> 

Aha, the disable depth for the I2C interrupt is 2 after
suspend_device_irq(), that's why there is no warning.

This should catch the bug and trigger the warning:

--- >8 ---
diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 453a8a0f4804..fe25104d8b22 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -653,6 +653,8 @@ void __enable_irq(struct irq_desc *desc)
 		break;
 	}
 	default:
+		if (desc->istate & IRQS_SUSPENDED)
+			goto err_out;
 		desc->depth--;
 	}
 }
--- >8 ---

Jon could you please give it a try? Will this change produce a warning
for the I2C driver on a PCIe suspend for the v5.6 kernel?