Re: call_usermodehelper hang

[Heiko Carstens]

> I have been running into some kernel hangs due to call_usermodehelper. 
Looking
> at the backtrace, it looks to me like there are deadlock issues with 
adding
> devices from work queues. Attached is a sample backtrace from one of the
> hangs I experienced. My question is why does call_usermodehelper do 
> 2 different
> things depending on whether or not it is called from the kevent 
> task? It appears
> that the simple way to fix the hang would be to never have 
call_usermodehelper
> use a work_queue since it must be called from process context anyway, or
> am I missing something?

Do you have a solution for this problem? As it appears we have the very 
same
problem with the zfcp lldd, since we also trigger a scsi_add_device call 
by
using schedule_work. IMO the right way to solve this problem would be to 
not
trigger any hotplug events while holding a semaphore.

> 0xc0000000017df300        1        0  0    0   D  0xc0000000017df7b0 
swapper
>            SP(esp)            PC(eip)      Function(args)
> 0xc00000003fc9f460  0x0000000000000000  NO_SYMBOL or Userspace
> 0xc00000003fc9f4f0  0xc000000000058c40  .schedule +0xb4
> 0xc00000003fc9f5c0  0xc00000000005a464  .wait_for_completion +0x138
> 0xc00000003fc9f6c0  0xc00000000007c594  .call_usermodehelper +0x104
> 0xc00000003fc9f810  0xc00000000022d3e8  .kobject_hotplug +0x3c4
> 0xc00000003fc9f900  0xc00000000022d67c  .kobject_add +0x134
> 0xc00000003fc9f9a0  0xc00000000012b3d8  .register_disk +0x70
> 0xc00000003fc9fa40  0xc00000000027dfe4  .add_disk +0x60
> 0xc00000003fc9fad0  0xc0000000002dc7dc  .sd_probe +0x290
> 0xc00000003fc9fb80  0xc00000000026fbe8  .bus_match +0x94
> 0xc00000003fc9fc10  0xc00000000026ff70  .driver_attach +0x8c
> 0xc00000003fc9fca0  0xc000000000270104  .bus_add_driver +0x110
> 0xc00000003fc9fd50  0xc000000000270a18  .driver_register +0x38
> 0xc00000003fc9fdd0  0xc0000000002cd8f8  .scsi_register_driver +0x28
> 0xc00000003fc9fe50  0xc0000000004941d8  .init_sd +0x8c
> 0xc00000003fc9fee0  0xc00000000000c720  .init +0x25c
> 0xc00000003fc9ff90  0xc0000000000183ec  .kernel_thread +0x4c
> 
> 0xc00000003fab3380        4        1  0    0   D  0xc00000003fab3830 
events/0
>            SP(esp)            PC(eip)      Function(args)
> 0xc00000003faaf6e0  0x0000000000000000  NO_SYMBOL or Userspace
> 0xc00000003faaf770  0xc000000000058c40  .schedule +0xb4
> 0xc00000003faaf840  0xc00000000022fa20  .rwsem_down_write_failed +0x14c
> 0xc00000003faaf910  0xc00000000026fed0  .bus_add_device +0x11c
> 0xc00000003faaf9b0  0xc00000000026e288  .device_add +0xd0
> 0xc00000003faafa50  0xc0000000002cdb00  .scsi_sysfs_add_sdev +0x8c
> 0xc00000003faafb00  0xc0000000002cbff8  .scsi_probe_and_add_lun +0xb04
> 0xc00000003faafc00  0xc0000000002ccca0  .scsi_add_device +0x90
> 0xc00000003faafcb0  0xc0000000002d9458  .ipr_worker_thread +0xc60
> 0xc00000003faafdc0  0xc00000000007cd9c  .worker_thread +0x268
> 0xc00000003faafee0  0xc0000000000839cc  .kthread +0x160
> 0xc00000003faaff90  0xc0000000000183ec  .kernel_thread +0x4c

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