Comment 10 for bug 1784665

I can recreate on upstream:

# uname -r; dmesg | tail -n 16
4.18.0-041800rc7-generic
[ 967.657492] INFO: task bcache_allocato:14240 blocked for more than 120 seconds.
[ 967.664138] Not tainted 4.18.0-041800rc7-generic #201807292230
[ 967.669641] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 967.673503] bcache_allocato D 0 14240 2 0x80000000
[ 967.673512] Call Trace:
[ 967.673529] __schedule+0x29e/0x840
[ 967.673535] ? reschedule_interrupt+0xa/0x20
[ 967.673539] schedule+0x2c/0x80
[ 967.673555] bch_bucket_alloc+0x19d/0x380 [bcache]
[ 967.673561] ? wait_woken+0x80/0x80
[ 967.673574] bch_prio_write+0x186/0x330 [bcache]
[ 967.673583] bch_allocator_thread+0x482/0xd10 [bcache]
[ 967.673589] kthread+0x120/0x140
[ 967.673598] ? bch_invalidate_one_bucket+0x80/0x80 [bcache]
[ 967.673601] ? kthread_bind+0x40/0x40
[ 967.673605] ret_from_fork+0x35/0x40