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Date:   Sun, 8 Jan 2017 21:42:22 +0100
From:   Clemens Gruber <clemens.gruber@...ruber.com>
To:     Bartosz Golaszewski <bgolaszewski@...libre.com>
Cc:     linux-gpio <linux-gpio@...r.kernel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Wolfram Sang <wsa@...-dreams.de>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: pca953x: lockdep warning since 4.10

On Sun, Jan 08, 2017 at 07:13:31PM +0100, Bartosz Golaszewski wrote:
> 2017-01-07 21:54 GMT+01:00 Clemens Gruber <clemens.gruber@...ruber.com>:
> > Hi,
> >
> > I observed the following lockdep warning when booting an i.MX6Q board
> > with several PCAL9555A gpio expanders connected over I2C. They are
> > connected to 3 separate busses, there is no i2c-mux in use.
> >
> > This warning appears with the latest mainline Linux kernel 4.10-rc2:
> >
> > [    0.671336] WARNING: CPU: 1 PID: 1 at kernel/locking/lockdep.c:3124 gpiochip_irq_map+0x44/0xa4
> > [    0.671347] DEBUG_LOCKS_WARN_ON(!key)
> > [    0.671359] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 4.10.0-rc2-00292-g7d08ba50fe02 #634
> > [    0.671372] Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree)
> > [    0.671403] [<8010ec90>] (unwind_backtrace) from [<8010bcf8>] (show_stack+0x10/0x14)
> > [    0.671427] [<8010bcf8>] (show_stack) from [<803bb6cc>] (dump_stack+0x98/0xc4)
> > [    0.671450] [<803bb6cc>] (dump_stack) from [<80128288>] (__warn+0xe0/0xfc)
> > [    0.671467] [<80128288>] (__warn) from [<801282e8>] (warn_slowpath_fmt+0x44/0x68)
> > [    0.671484] [<801282e8>] (warn_slowpath_fmt) from [<803ee848>] (gpiochip_irq_map+0x44/0xa4)
> > [    0.671504] [<803ee848>] (gpiochip_irq_map) from [<80191178>] (irq_domain_associate+0x74/0x1d4)
> > [    0.671523] [<80191178>] (irq_domain_associate) from [<801918e8>] (irq_create_mapping+0x64/0xc8)
> > [    0.671541] [<801918e8>] (irq_create_mapping) from [<803ef9d4>] (_gpiochip_irqchip_add+0xdc/0x1a4)
> > [    0.671562] [<803ef9d4>] (_gpiochip_irqchip_add) from [<803f54c0>] (pca953x_probe+0x45c/0x614)
> > [    0.671585] [<803f54c0>] (pca953x_probe) from [<804e22bc>] (i2c_device_probe+0x14c/0x1e0)
> > [    0.671608] [<804e22bc>] (i2c_device_probe) from [<8043e368>] (really_probe+0x1c8/0x260)
> > [    0.671625] [<8043e368>] (really_probe) from [<8043cf74>] (bus_for_each_drv+0x74/0xb8)
> > [    0.671642] [<8043cf74>] (bus_for_each_drv) from [<8043e6dc>] (__device_attach+0xc0/0x104)
> > [    0.671658] [<8043e6dc>] (__device_attach) from [<8043d1c0>] (bus_probe_device+0x88/0x90)
> > [    0.671675] [<8043d1c0>] (bus_probe_device) from [<8043b80c>] (device_add+0x410/0x598)
> > [    0.671692] [<8043b80c>] (device_add) from [<804e1364>] (i2c_new_device+0x164/0x1c0)
> > [    0.671707] [<804e1364>] (i2c_new_device) from [<804e1830>] (i2c_register_adapter+0x280/0x58c)
> > [    0.671727] [<804e1830>] (i2c_register_adapter) from [<804e6178>] (i2c_imx_probe+0x33c/0x568)
> > [    0.671747] [<804e6178>] (i2c_imx_probe) from [<8043f848>] (platform_drv_probe+0x34/0x6c)
> > [    0.671764] [<8043f848>] (platform_drv_probe) from [<8043e368>] (really_probe+0x1c8/0x260)
> > [    0.671779] [<8043e368>] (really_probe) from [<8043e4cc>] (__driver_attach+0xcc/0xd0)
> > [    0.671796] [<8043e4cc>] (__driver_attach) from [<8043ca34>] (bus_for_each_dev+0x7c/0xc0)
> > [    0.671812] [<8043ca34>] (bus_for_each_dev) from [<8043d3d8>] (bus_add_driver+0x108/0x208)
> > [    0.671830] [<8043d3d8>] (bus_add_driver) from [<8043ee28>] (driver_register+0x78/0xf4)
> > [    0.671851] [<8043ee28>] (driver_register) from [<80900e20>] (do_one_initcall+0xc4/0x184)
> > [    0.671868] [<80900e20>] (do_one_initcall) from [<8090103c>] (kernel_init_freeable+0x15c/0x1ec)
> > [    0.671886] [<8090103c>] (kernel_init_freeable) from [<806e4c8c>] (kernel_init+0x8/0x10c)
> > [    0.671905] [<806e4c8c>] (kernel_init) from [<801079d0>] (ret_from_fork+0x14/0x24)
> > [    0.671922] ---[ end trace f719aac79da5d26a ]---
> >
> > Is this a false positive?
> >
> > Regards,
> > Clemens
> 
> Hi Clemens,
> 
> can you revert commit 559b46990e76 ("gpio: pca953x: fix an incorrect
> lockdep warning") and check if you still get the warnings?
> 
> Thanks,
> Bartosz Golaszewski

Hi Bartosz,

reverting that commit, which added the lockdep_set_subclass call, had no
effect.

However, I ran git bisect and found out that reverting commit
d245b3f9bd36 ("gpio: simplify adding threaded interrupts") makes the
warning disappear.

Regards,
Clemens

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