Issue

Example: an strace of creating a snapshot of the /tmp file system and storing the result in /tmp

# strace -o /tmp/lvcreate.strace lvcreate -s -L1G -n tmp-snap lv_tmp vg_root

The hung tasks, strace and lvcreate, will have the following backtrace:

Jun  3 10:34:02 dhcp-26-137 kernel: strace        D ffff88004bd07cb8  5032  5749   1971 0x00000080
Jun  3 10:34:02 dhcp-26-137 kernel: ffff88004bd07c58 0000000000000046 ffff88004bd07be8 ffff88004d651860
Jun  3 10:34:02 dhcp-26-137 kernel: ffff88004d651878 0000000000000046 0000000000000001 0000000000000286
Jun  3 10:34:02 dhcp-26-137 kernel: ffff88002ee21e80 ffff88004bd07fd8 000000000000fd28 ffff88002ee21e80
Jun  3 10:34:02 dhcp-26-137 kernel: Call Trace:
Jun  3 10:34:02 dhcp-26-137 kernel: [<ffffffff8109bfde>] ? prepare_to_wait+0x4e/0x80
Jun  3 10:34:02 dhcp-26-137 kernel: [<ffffffff8119fc72>] __sb_start_write+0x1e2/0x210
Jun  3 10:34:02 dhcp-26-137 kernel: [<ffffffff8109bcf0>] ? autoremove_wake_function+0x0/0x40
Jun  3 10:34:02 dhcp-26-137 kernel: [<ffffffff81130cc9>] generic_file_aio_write+0x69/0x100
Jun  3 10:34:02 dhcp-26-137 kernel: [<ffffffffa04e8014>] ext4_file_write+0x64/0x1e0 [ext4]
Jun  3 10:34:02 dhcp-26-137 kernel: [<ffffffff810581b2>] ? task_rq_lock+0x62/0xb0
Jun  3 10:34:02 dhcp-26-137 kernel: [<ffffffff8119d50a>] do_sync_write+0xfa/0x140
Jun  3 10:34:02 dhcp-26-137 kernel: [<ffffffff810b513d>] ? trace_hardirqs_on+0xd/0x10
Jun  3 10:34:02 dhcp-26-137 kernel: [<ffffffff8109bcf0>] ? autoremove_wake_function+0x0/0x40
Jun  3 10:34:02 dhcp-26-137 kernel: [<ffffffff8124826b>] ? selinux_file_permission+0xfb/0x150
Jun  3 10:34:02 dhcp-26-137 kernel: [<ffffffff8123c6b6>] ? security_file_permission+0x16/0x20
Jun  3 10:34:02 dhcp-26-137 kernel: [<ffffffff8119d808>] vfs_write+0xb8/0x1a0
Jun  3 10:34:02 dhcp-26-137 kernel: [<ffffffff8119e101>] sys_write+0x51/0x90
Jun  3 10:34:02 dhcp-26-137 kernel: [<ffffffff8100b072>] system_call_fastpath+0x16/0x1b
Jun  3 10:34:02 dhcp-26-137 kernel: lvcreate      t 0000000000000005  4472  5752   5749 0x00000081
Jun  3 10:34:02 dhcp-26-137 kernel: ffff88002ee37e58 0000000000000046 ffffffff8156e560 ffffffff810e36eb
Jun  3 10:34:02 dhcp-26-137 kernel: ffff88002ee37dd8 0000000000000246 ffffffff81851018 ffffffff81851000
Jun  3 10:34:02 dhcp-26-137 kernel: ffff880037e79f00 ffff88002ee37fd8 000000000000fd28 ffff880037e79f00
Jun  3 10:34:02 dhcp-26-137 kernel: Call Trace:
Jun  3 10:34:02 dhcp-26-137 kernel: [<ffffffff810e36eb>] ? do_ptrace_notify_stop+0x2b/0x70
Jun  3 10:34:02 dhcp-26-137 kernel: [<ffffffff810e370b>] ? do_ptrace_notify_stop+0x4b/0x70
Jun  3 10:34:02 dhcp-26-137 kernel: [<ffffffff810e1142>] utrace_stop+0xf2/0x1d0
Jun  3 10:34:02 dhcp-26-137 kernel: [<ffffffff810e1267>] finish_resume_report+0x47/0x100
Jun  3 10:34:02 dhcp-26-137 kernel: [<ffffffff810e13b0>] utrace_resume+0x90/0x130
Jun  3 10:34:02 dhcp-26-137 kernel: [<ffffffff8100aaa0>] do_notify_resume+0xb0/0xc0
Jun  3 10:34:02 dhcp-26-137 kernel: [<ffffffff8100b3c4>] int_signal+0x12/0x17