[PATCH] drm/exynos: fix infinite loop issue incurred by no pair

[Inki Dae]

On 2014년 11월 18일 19:23, Javier Martinez Canillas wrote:
> Hello Inki,
> 
>> Right, but at least, we could avoid kernel booting failure which is very
>> critical. Please know that this patch is temporary to avoid the kernel
>> booting failure although deferred probe request of Exynos drm could be
>> broken. For this, I will look into dd core to find out more generic way:
>> I suspect that this might be incurred in case that a driver is probed in
>> probe context of other driver or it might be really dd core bug.
>>
> 
> I gave a try to your patch on top of today's linux-next and I still
> see the same boot failure reported by Kevin on a Exynos5420 Peach Pit
> so $subject does not fix the issue. The boot message is [0] fyi.
> 
> By digging a bit I noticed that this happens when the
> exynos_drm_platform_probe() calls platform_driver_register() to
> register the Exynos fimd platform driver. The problem is that in
> __driver_attach() the call to device_lock(dev->parent) never returns
> and the thread sleeps forever waiting for the device parent mutex to
> be released.
> 
> Do you have any ideas why this could happen?

As I mentioned above, I guess this issue could be incurred when a driver
is probed in probe context of other driver. Actually, we had faced with
same issue but we couldn't see this issue anymore for some time. Anyway,
we need more checking.

Thanks,
Inki Dae

> 
> If I modify __driver_attach() to only grab the device lock and not its
> parent lock, then the thread is able to hold its own mutex and the
> platform driver registration succeeds but then I see the infinite loop
> that was reported before and the workaround in $subject indeed avoids
> to happen.
> 
> So we have two issues here and your patch is only a workaround for the later.
> 
> Best regards,
> Javier
> 
> [0]:
> [    1.324091] [drm] Initialized drm 1.1.0 20060810
> [  240.158665] random: nonblocking pool is initialized
> [  240.162202] INFO: task swapper/0:1 blocked for more than 120 seconds.
> [  240.168493]       Not tainted 3.18.0-rc4-next-20141117-00001-g85466f9 #22
> [  240.175256] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
> disables this message.
> [  240.183064] swapper/0       D c045bb00     0     1      0 0x00000000
> [  240.189410] [<c045bb00>] (__schedule) from [<c045c230>]
> (schedule_preempt_disabled+0x14/0x20)
> [  240.197904] [<c045c230>] (schedule_preempt_disabled) from
> [<c045e998>] (__mutex_lock_slowpath+0x19c/0x3f4)
> [  240.207531] [<c045e998>] (__mutex_lock_slowpath) from [<c045ebfc>]
> (mutex_lock+0xc/0x24)
> [  240.215599] [<c045ebfc>] (mutex_lock) from [<c0281718>]
> (__driver_attach+0x44/0x90)
> [  240.223239] [<c0281718>] (__driver_attach) from [<c027ff30>]
> (bus_for_each_dev+0x54/0x88)
> [  240.231387] [<c027ff30>] (bus_for_each_dev) from [<c0280da0>]
> (bus_add_driver+0xd8/0x1cc)
> [  240.239541] [<c0280da0>] (bus_add_driver) from [<c0281d80>]
> (driver_register+0x78/0xf4)
> [  240.247523] [<c0281d80>] (driver_register) from [<c0274324>]
> (exynos_drm_platform_probe+0x34/0x188)
> [  240.256546] [<c0274324>] (exynos_drm_platform_probe) from
> [<c02829d8>] (platform_drv_probe+0x48/0x98)
> [  240.265739] [<c02829d8>] (platform_drv_probe) from [<c02815b4>]
> (driver_probe_device+0x114/0x234)
> [  240.274588] [<c02815b4>] (driver_probe_device) from [<c0281760>]
> (__driver_attach+0x8c/0x90)
> [  240.283003] [<c0281760>] (__driver_attach) from [<c027ff30>]
> (bus_for_each_dev+0x54/0x88)
> [  240.291158] [<c027ff30>] (bus_for_each_dev) from [<c0280da0>]
> (bus_add_driver+0xd8/0x1cc)
> [  240.299311] [<c0280da0>] (bus_add_driver) from [<c0281d80>]
> (driver_register+0x78/0xf4)
> [  240.307293] [<c0281d80>] (driver_register) from [<c02742a4>]
> (exynos_drm_init+0x84/0xd0)
> [  240.315362] [<c02742a4>] (exynos_drm_init) from [<c0008944>]
> (do_one_initcall+0x80/0x1d0)
> [  240.323521] [<c0008944>] (do_one_initcall) from [<c0624d3c>]
> (kernel_init_freeable+0x108/0x1d4)
> [  240.332191] [<c0624d3c>] (kernel_init_freeable) from [<c0457224>]
> (kernel_init+0x8/0xe4)
> [  240.340261] [<c0457224>] (kernel_init) from [<c000e638>]
> (ret_from_fork+0x14/0x3c)
> --
> To unsubscribe from this list: send the line "unsubscribe linux-samsung-soc" in
> the body of a message to majordomo at vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>