kcompactd hang during memory offlining

[Reza Arbab]

Assume memory47 is the last online block left in node1. This will hang:

# echo offline > /sys/devices/system/node/node1/memory47/state

After a couple of minutes, the following pops up in dmesg:

INFO: task bash:957 blocked for more than 120 seconds.
      Not tainted 4.6.0-rc6+ #6
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
bash            D ffff8800b7adbaf8     0   957    951 0x00000000
 ffff8800b7adbaf8 ffff880034d5b880 ffff8800b698d4c0 ffff8800b7adc000
 7fffffffffffffff ffff88003381ff10 ffff8800b698d4c0 0000000000180000
 ffff8800b7adbb10 ffffffff817be0b5 ffff88003381ff08 ffff8800b7adbbc0
Call Trace:
 [<ffffffff817be0b5>] schedule+0x35/0x80
 [<ffffffff817c100c>] schedule_timeout+0x1ac/0x270
 [<ffffffff810d9750>] ? check_preempt_wakeup+0x100/0x220
 [<ffffffff810ce0a0>] ? check_preempt_curr+0x80/0x90
 [<ffffffff817bf501>] wait_for_completion+0xe1/0x120
 [<ffffffff810cefc0>] ? wake_up_q+0x70/0x70
 [<ffffffff810c42ff>] kthread_stop+0x4f/0x110
 [<ffffffff811e1046>] kcompactd_stop+0x26/0x40
 [<ffffffff817b7a16>] __offline_pages.constprop.28+0x7e6/0x840
 [<ffffffff8121ee61>] offline_pages+0x11/0x20
 [<ffffffff8151a073>] memory_block_action+0x73/0x1d0
 [<ffffffff8151a217>] memory_subsys_offline+0x47/0x60
 [<ffffffff81502dc6>] device_offline+0x86/0xb0
 [<ffffffff8151a8fa>] store_mem_state+0xda/0xf0
 [<ffffffff814ffea8>] dev_attr_store+0x18/0x30
 [<ffffffff812c1097>] sysfs_kf_write+0x37/0x40
 [<ffffffff812c062d>] kernfs_fop_write+0x11d/0x170
 [<ffffffff8123e797>] __vfs_write+0x37/0x120
 [<ffffffff8134d1ad>] ? security_file_permission+0x3d/0xc0
 [<ffffffff810eed32>] ? percpu_down_read+0x12/0x50
 [<ffffffff8123f969>] vfs_write+0xa9/0x1a0
 [<ffffffff8134d543>] ? security_file_fcntl+0x43/0x60
 [<ffffffff81240dc5>] SyS_write+0x55/0xc0
 [<ffffffff817c21b2>] entry_SYSCALL_64_fastpath+0x1a/0xa4

Bisect ends on commit 698b1b306 ("mm, compaction: introduce kcompactd").

--
Reza Arbab