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? 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)
