system hung up when offlining CPUs

[YASUAKI ISHIMATSU]

Hi Thomas,

When offlining all CPUs except cpu0, system hung up with the following message.

[...] INFO: task kworker/u384:1:1234 blocked for more than 120 seconds.
[...]       Not tainted 4.12.0-rc6+ #19
[...] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[...] kworker/u384:1  D    0  1234      2 0x00000000
[...] Workqueue: writeback wb_workfn (flush-253:0)
[...] Call Trace:
[...]  __schedule+0x28a/0x880
[...]  schedule+0x36/0x80
[...]  schedule_timeout+0x249/0x300
[...]  ? __schedule+0x292/0x880
[...]  __down_common+0xfc/0x132
[...]  ? _xfs_buf_find+0x2bb/0x510 [xfs]
[...]  __down+0x1d/0x1f
[...]  down+0x41/0x50
[...]  xfs_buf_lock+0x3c/0xf0 [xfs]
[...]  _xfs_buf_find+0x2bb/0x510 [xfs]
[...]  xfs_buf_get_map+0x2a/0x280 [xfs]
[...]  xfs_buf_read_map+0x2d/0x180 [xfs]
[...]  xfs_trans_read_buf_map+0xf5/0x310 [xfs]
[...]  xfs_btree_read_buf_block.constprop.35+0x78/0xc0 [xfs]
[...]  xfs_btree_lookup_get_block+0x88/0x160 [xfs]
[...]  xfs_btree_lookup+0xd0/0x3b0 [xfs]
[...]  ? xfs_allocbt_init_cursor+0x41/0xe0 [xfs]
[...]  xfs_alloc_ag_vextent_near+0xaf/0xaa0 [xfs]
[...]  xfs_alloc_ag_vextent+0x13c/0x150 [xfs]
[...]  xfs_alloc_vextent+0x425/0x590 [xfs]
[...]  xfs_bmap_btalloc+0x448/0x770 [xfs]
[...]  xfs_bmap_alloc+0xe/0x10 [xfs]
[...]  xfs_bmapi_write+0x61d/0xc10 [xfs]
[...]  ? kmem_zone_alloc+0x96/0x100 [xfs]
[...]  xfs_iomap_write_allocate+0x199/0x3a0 [xfs]
[...]  xfs_map_blocks+0x1e8/0x260 [xfs]
[...]  xfs_do_writepage+0x1ca/0x680 [xfs]
[...]  write_cache_pages+0x26f/0x510
[...]  ? xfs_vm_set_page_dirty+0x1d0/0x1d0 [xfs]
[...]  ? blk_mq_dispatch_rq_list+0x305/0x410
[...]  ? deadline_remove_request+0x7d/0xc0
[...]  xfs_vm_writepages+0xb6/0xd0 [xfs]
[...]  do_writepages+0x1c/0x70
[...]  __writeback_single_inode+0x45/0x320
[...]  writeback_sb_inodes+0x280/0x570
[...]  __writeback_inodes_wb+0x8c/0xc0
[...]  wb_writeback+0x276/0x310
[...]  ? get_nr_dirty_inodes+0x4d/0x80
[...]  wb_workfn+0x2d4/0x3b0
[...]  process_one_work+0x149/0x360
[...]  worker_thread+0x4d/0x3c0
[...]  kthread+0x109/0x140
[...]  ? rescuer_thread+0x380/0x380
[...]  ? kthread_park+0x60/0x60
[...]  ret_from_fork+0x25/0x30


I bisected upstream kernel. And I found that the following commit lead
the issue.

commit c5cb83bb337c25caae995d992d1cdf9b317f83de
Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Date:   Tue Jun 20 01:37:51 2017 +0200

    genirq/cpuhotplug: Handle managed IRQs on CPU hotplug


Thanks,
Yasuaki Ishimatsu