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Subjectcall_usermodehelper hang
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?

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

Brian King
eServer Storage I/O
IBM Linux Technology Center

Brian King
eServer Storage I/O
IBM Linux Technology Center

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