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Subject: Re: Odroid U3 mutex deadlock.
To: Anand Moon <linux.amoon@gmail.com>,
        "linux-samsung-soc@vger.kernel.org" 
	<linux-samsung-soc@vger.kernel.org>
References: <CANAwSgSE4UE5jn4Rp0LfVhDcSP=ynDsbCaUSHmM31_MF849bSw@mail.gmail.com>
Cc: Linux Kernel <linux-kernel@vger.kernel.org>,
        Javier Martinez Canillas <javier@osg.samsung.com>,
        Kukjin Kim <kgene@kernel.org>, linux-arm-kernel@lists.infradead.org
From: Krzysztof Kozlowski <k.kozlowski@samsung.com>
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On 12.12.2015 13:32, Anand Moon wrote:
> Hi Krzysztof,
> 
> I am just observing this deadlock om my Odroid U3.

This is not a deadlock yet, just a report from lockdep. Could be a real
issue, could be false positive, maybe some locks miss nesting annotations.

Typical information for bug report would be useful, like the exact
version (it is mentioned in lockdep report but is it really correct?)
and reproducibility. And of course git-bisect would be nice to have, see:
Documentation/BUG-HUNTING

Best regards,
Krzysztof


> ------------------------------------------------------------------------------------------------------------------
> 
> [    2.937531] =============================================
> [    2.938733] [ INFO: possible recursive locking detected ]
> [    2.944117] 4.4.0-rc4-xu3s #32 Not tainted
> [    2.948195] ---------------------------------------------
> [    2.953577] swapper/0/1 is trying to acquire lock:
> [    2.958351]  (&genpd->lock){+.+...}, at: [<c0361550>]
> __genpd_poweron+0x64/0x108
> [    2.965727]
> [    2.965727] but task is already holding lock:
> [    2.971543]  (&genpd->lock){+.+...}, at: [<c0361af8>]
> genpd_dev_pm_attach+0x168/0x1b8
> [    2.979355]
> [    2.979355] other info that might help us debug this:
> [    2.985865]  Possible unsafe locking scenario:
> [    2.985865]
> [    2.991768]        CPU0
> [    2.994198]        ----
> [    2.996628]   lock(&genpd->lock);
> [    2.999926]   lock(&genpd->lock);
> [    3.003225]
> [    3.003225]  *** DEADLOCK ***
> [    3.003225]
> [    3.009128]  May be due to missing lock nesting notation
> [    3.009128]
> [    3.015900] 3 locks held by swapper/0/1:
> [    3.019804]  #0:  (&dev->mutex){......}, at: [<c0350910>]
> __driver_attach+0x48/0x98
> [    3.027442]  #1:  (&dev->mutex){......}, at: [<c0350920>]
> __driver_attach+0x58/0x98
> [    3.035081]  #2:  (&genpd->lock){+.+...}, at: [<c0361af8>]
> genpd_dev_pm_attach+0x168/0x1b8
> [    3.043326]
> [    3.043326] stack backtrace:
> [    3.047671] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.4.0-rc4-xu3s #32
> [    3.054351] Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
> [    3.060444] [<c0016c98>] (unwind_backtrace) from [<c00139c4>]
> (show_stack+0x10/0x14)
> [    3.068163] [<c00139c4>] (show_stack) from [<c0270df0>]
> (dump_stack+0x84/0xc4)
> [    3.075367] [<c0270df0>] (dump_stack) from [<c00780b8>]
> (__lock_acquire+0x1f88/0x215c)
> [    3.083262] [<c00780b8>] (__lock_acquire) from [<c007886c>]
> (lock_acquire+0xa4/0xd0)
> [    3.090990] [<c007886c>] (lock_acquire) from [<c0641f2c>]
> (mutex_lock_nested+0x70/0x4d4)
> [    3.099061] [<c0641f2c>] (mutex_lock_nested) from [<c0361550>]
> (__genpd_poweron+0x64/0x108)
> [    3.107393] [<c0361550>] (__genpd_poweron) from [<c0361b00>]
> (genpd_dev_pm_attach+0x170/0x1b8)
> [    3.115986] [<c0361b00>] (genpd_dev_pm_attach) from [<c03520a8>]
> (platform_drv_probe+0x2c/0xac)
> [    3.124667] [<c03520a8>] (platform_drv_probe) from [<c03507d4>]
> (driver_probe_device+0x208/0x2fc)
> [    3.133519] [<c03507d4>] (driver_probe_device) from [<c035095c>]
> (__driver_attach+0x94/0x98)
> [    3.141939] [<c035095c>] (__driver_attach) from [<c034ec14>]
> (bus_for_each_dev+0x68/0x9c)
> [    3.150097] [<c034ec14>] (bus_for_each_dev) from [<c034fec8>]
> (bus_add_driver+0x1a0/0x218)
> [    3.158344] [<c034fec8>] (bus_add_driver) from [<c035115c>]
> (driver_register+0x78/0xf8)
> [    3.166330] [<c035115c>] (driver_register) from [<c0338488>]
> (exynos_drm_register_drivers+0x28/0x74)
> [    3.175441] [<c0338488>] (exynos_drm_register_drivers) from
> [<c0338594>] (exynos_drm_init+0x6c/0xc4)
> [    3.184556] [<c0338594>] (exynos_drm_init) from [<c00097f4>]
> (do_one_initcall+0x90/0x1dc)
> [    3.192718] [<c00097f4>] (do_one_initcall) from [<c0895e08>]
> (kernel_init_freeable+0x158/0x1f8)
> [    3.201396] [<c0895e08>] (kernel_init_freeable) from [<c063ecac>]
> (kernel_init+0x8/0xe8)
> [    3.209469] [<c063ecac>] (kernel_init) from [<c000f7d0>]
> (ret_from_fork+0x14/0x24)
> [    3.217932] exynos-hdmi 12d00000.hdmi: GPIO lookup for consumer hpd
> [    3.223293] exynos-hdmi 12d00000.hdmi: using device tree for GPIO lookup
> [    3.229980] of_get_named_gpiod_flags: can't parse 'hpd-gpios'
> property of node '/hdmi@12D00000[0]'
> [    3.238945] of_get_named_gpiod_flags: parsed 'hpd-gpio' property of
> node '/hdmi@12D00000[0]' - status (0)
> [    3.253430] exynos-drm exynos-drm: bound 12c10000.mixer (ops
> mixer_component_ops)
> [    3.256216] exynos-drm exynos-drm: bound 12d00000.hdmi (ops
> hdmi_component_ops)
> [    3.263245] [drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
> [    3.269812] [drm] No driver support for vblank timestamp query.
> [    3.323251] exynos-drm exynos-drm: fb0:  frame buffer device
> [    3.341464] [drm] Initialized exynos 1.0.0 20110530 on minor 0
> 
> -----------------------------------------------------------------------------------------------------------------------
> -Anand Moon
> 
>