linux-kernel - Re: [PATCH 06/14] extcon: arizona: Fix various races on driver unbind

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Date:   Tue, 29 Dec 2020 12:10:37 +0000
From:   Charles Keepax <ckeepax@...nsource.cirrus.com>
To:     Hans de Goede <hdegoede@...hat.com>
CC:     Lee Jones <lee.jones@...aro.org>,
        MyungJoo Ham <myungjoo.ham@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Cezary Rojewski <cezary.rojewski@...el.com>,
        Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        Liam Girdwood <liam.r.girdwood@...ux.intel.com>,
        Jie Yang <yang.jie@...ux.intel.com>,
        Mark Brown <broonie@...nel.org>,
        <patches@...nsource.cirrus.com>, <linux-kernel@...r.kernel.org>,
        <alsa-devel@...a-project.org>
Subject: Re: [PATCH 06/14] extcon: arizona: Fix various races on driver unbind

On Sun, Dec 27, 2020 at 10:12:24PM +0100, Hans de Goede wrote:
> We must free/disable all interrupts and cancel all pending works
> before doing further cleanup.
> 
> Before this commit arizona_extcon_remove() was doing several
> register writes to shut things down before disabling the IRQs
> and it was cancelling only 1 of the 3 different works used.
> 
> Move all the register-writes shutting things down to after
> the disabling of the IRQs and add the 2 missing
> cancel_delayed_work_sync() calls.
> 
> This fixes various possible races on driver unbind. One of which
> would always trigger on devices using the mic-clamp feature for
> jack detection. The ARIZONA_MICD_CLAMP_MODE_MASK update was
> done before disabling the IRQs, causing:
> 1. arizona_jackdet() to run
> 2. detect a jack being inserted (clamp disabled means jack inserted)
> 3. call arizona_start_mic() which:
> 3.1 Enables the MICVDD regulator
> 3.2 takes a pm_runtime_reference
> 
> And this was all happening after the ARIZONA_MICD_ENA bit clearing,
> which would undo 3.1 and 3.2 because the ARIZONA_MICD_CLAMP_MODE_MASK
> update was being done after the ARIZONA_MICD_ENA bit clearing.
> 
> So this means that arizona_extcon_remove() would exit with
> 1. MICVDD enabled and 2. The pm_runtime_reference being unbalanced.
> 
> MICVDD still being enabled caused the following oops when the
> regulator is released by the devm framework:
> 
> [ 2850.745757] ------------[ cut here ]------------
> [ 2850.745827] WARNING: CPU: 2 PID: 2098 at drivers/regulator/core.c:2123 _regulator_put.part.0+0x19f/0x1b0
> [ 2850.745835] Modules linked in: extcon_arizona ...
> ...
> [ 2850.746909] Call Trace:
> [ 2850.746932]  regulator_put+0x2d/0x40
> [ 2850.746946]  release_nodes+0x22a/0x260
> [ 2850.746984]  __device_release_driver+0x190/0x240
> [ 2850.747002]  driver_detach+0xd4/0x120
> ...
> [ 2850.747337] ---[ end trace f455dfd7abd9781f ]---
> 
> Note this oops is just one of various theoretically possible races caused
> by the wrong ordering inside arizona_extcon_remove(), this fixes the
> ordering fixing all possible races, including the reported oops.
> 
> Signed-off-by: Hans de Goede <hdegoede@...hat.com>
> ---

Sorry yes there are a few rough corners on the extcon stuff, I
have clean up series I have been working on as part of
upstreaming the Madera extcon hopefully I will get that sent out
one day.

Acked-by: Charles Keepax <ckeepax@...nsource.cirrus.com>

Thanks,
Charles