linux-kernel - Re: [PATCH v2 2/3] bq2415x_charger: Use power

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Message-ID: <CAOf5uw=yEhOACDMbdWCFYkGC6dwS6_KweqHcTDOuFmETzN5QPg@mail.gmail.com>
Date:	Sun, 19 Jan 2014 21:56:15 +0100
From:	Michael Trimarchi <michael@...rulasolutions.com>
To:	Pali Rohár <pali.rohar@...il.com>,
	Anton Vorontsov <anton@...msg.org>,
	Michael Trimarchi <michael@...rulasolutions.com>,
	David Woodhouse <dwmw2@...radead.org>,
	Tony Lindgren <tony@...mide.com>,
	Russell King <linux@....linux.org.uk>,
	linux-kernel@...r.kernel.org,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	freemangordon@....bg, aaro.koskinen@....fi, pavel@....cz
Subject: Re: [PATCH v2 2/3] bq2415x_charger: Use power_supply notifier for automode

Hi

On Sun, Jan 19, 2014 at 9:54 PM, Sebastian Reichel <sre@...g0.de> wrote:
> On Mon, Dec 02, 2013 at 02:45:06AM +0100, Michael Trimarchi wrote:
>> On Mon, Dec 2, 2013 at 1:24 AM, Anton Vorontsov <anton@...msg.org> wrote:
>> > On Mon, Dec 02, 2013 at 01:02:40AM +0100, Michael Trimarchi wrote:
>> >> On Sun, Dec 1, 2013 at 11:37 PM, Anton Vorontsov <anton@...msg.org> wrote:
>> >> > On Mon, Nov 25, 2013 at 08:16:34PM +0100, Michael Trimarchi wrote:
>> >> > ...
>> >> >> >> So you can read this value without any type of synchronization
>> >> >> >> with the power_supply_core
>> >> >> >> and sysfs implementation?
>> >> > ...
>> >> >> https://lists.ubuntu.com/archives/kernel-team/2013-January/025206.html
>> >> >>
>> >> >> I found and equivalent scenario that I was trying to said
>> >> >
>> >> > That's a good question, actually. Even though in Pali's case the notifier
>> >> > is atomic (so that we are pretty confident that the object won't be
>> >> > unregistered), there is still a possiblity of a dead lock, for example. So
>> >>
>> >> So if the get_property is a sleeping function it will be a deadlock. Right?
>> >
>> > All kind of bad things might happen, yes. But before that I would expect a
>> > bunch of warnings from might_sleep() stuff.
>> >
>> > I would recommend to test the patches using preempt/smp kernels + various
>> > DEBUG_ kernel options set.
>> >
>>
>> Is it more simple to make it not atomic and use a mutex in get_property?
>
> I just built a kernel with CONFIG_DEBUG_ATOMIC_SLEEP to test another
> driver and got the following output for bq2415x:
>
> [    7.667449] Workqueue: events power_supply_changed_work
> [    7.673034] [<c0015c28>] (unwind_backtrace+0x0/0xe0) from [<c0011e1c>] (show_stack+0x10/0x14)
> [    7.682098] [<c0011e1c>] (show_stack+0x10/0x14) from [<c052cdd0>] (dump_stack+0x78/0xac)
> [    7.690704] [<c052cdd0>] (dump_stack+0x78/0xac) from [<c052a044>] (__schedule_bug+0x48/0x60)
> [    7.699645] [<c052a044>] (__schedule_bug+0x48/0x60) from [<c053071c>] (__schedule+0x74/0x638)
> [    7.708618] [<c053071c>] (__schedule+0x74/0x638) from [<c05301fc>] (schedule_timeout+0x1dc/0x24c)
> [    7.718017] [<c05301fc>] (schedule_timeout+0x1dc/0x24c) from [<c05316ec>] (wait_for_common+0x138/0x17c)
> [    7.727966] [<c05316ec>] (wait_for_common+0x138/0x17c) from [<c0362a70>] (omap_i2c_xfer+0x340/0x4a0)
> [    7.737640] [<c0362a70>] (omap_i2c_xfer+0x340/0x4a0) from [<c035d928>] (__i2c_transfer+0x40/0x74)
> [    7.747039] [<c035d928>] (__i2c_transfer+0x40/0x74) from [<c035e22c>] (i2c_transfer+0x6c/0x90)
> [    7.756195] [<c035e22c>] (i2c_transfer+0x6c/0x90) from [<c037ad24>] (bq2415x_i2c_write+0x48/0x78)
> [    7.765563] [<c037ad24>] (bq2415x_i2c_write+0x48/0x78) from [<c037ae60>] (bq2415x_set_weak_battery_voltage+0x4c/0x50)
> [    7.776824] [<c037ae60>] (bq2415x_set_weak_battery_voltage+0x4c/0x50) from [<c037bce8>] (bq2415x_set_mode+0xdc/0x14c)
> [    7.788085] [<c037bce8>] (bq2415x_set_mode+0xdc/0x14c) from [<c037bfb8>] (bq2415x_notifier_call+0xa8/0xb4)
> [    7.798309] [<c037bfb8>] (bq2415x_notifier_call+0xa8/0xb4) from [<c005f228>] (notifier_call_chain+0x38/0x68)
> [    7.808715] [<c005f228>] (notifier_call_chain+0x38/0x68) from [<c005f284>] (__atomic_notifier_call_chain+0x2c/0x3c)
> [    7.819732] [<c005f284>] (__atomic_notifier_call_chain+0x2c/0x3c) from [<c005f2a8>] (atomic_notifier_call_chain+0x14/0x18)
> [    7.831420] [<c005f2a8>] (atomic_notifier_call_chain+0x14/0x18) from [<c0378078>] (power_supply_changed_work+0x6c/0xb8)
> [    7.842864] [<c0378078>] (power_supply_changed_work+0x6c/0xb8) from [<c00556c0>] (process_one_work+0x248/0x440)
> [    7.853546] [<c00556c0>] (process_one_work+0x248/0x440) from [<c0055d6c>] (worker_thread+0x208/0x350)
> [    7.863372] [<c0055d6c>] (worker_thread+0x208/0x350) from [<c005b0ac>] (kthread+0xc8/0xdc)
> [    7.872131] [<c005b0ac>] (kthread+0xc8/0xdc) from [<c000e138>] (ret_from_fork+0x14/0x3c)
>
> -- Sebastian


I have already give my opinion about this problem

Michael
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