I/O threads hang in bt_get

Issue

• I/O threads hang in bt_get
• Following trace seen:

 #0 [ffff883b572af730] __schedule at ffffffff8168b485
 #1 [ffff883b572af798] schedule at ffffffff8168bad9
 #2 [ffff883b572af7a8] schedule_timeout at ffffffff81689529
 #3 [ffff883b572af850] io_schedule_timeout at ffffffff8168b07e
 #4 [ffff883b572af880] io_schedule at ffffffff8168b118
 #5 [ffff883b572af890] bt_get at ffffffff812fb2e5
 #6 [ffff883b572af900] blk_mq_get_tag at ffffffff812fb84f
 #7 [ffff883b572af928] __blk_mq_alloc_request at ffffffff812f6c2b
 #8 [ffff883b572af958] blk_mq_map_request at ffffffff812f90a1
 #9 [ffff883b572af9c8] blk_sq_make_request at ffffffff812f9e00
#10 [ffff883b572afa50] generic_make_request at ffffffff812ee8a9
#11 [ffff883b572afa98] submit_bio at ffffffff812ee9f1
#12 [ffff883b572afaf0] cxiStartIO at ffffffffa09cb9ac [mmfslinux]
#13 [ffff883b572afc28] _ZN9DiskSched7localIOEPP15MBDoDiskIOParmsiiP15KernelOperation at ffffffffa0b31158 [mmfs26]
#14 [ffff883b572afcf8] kxLocalIO at ffffffffa0b317b2 [mmfs26]
#15 [ffff883b572afd58] _Z8ss_ioctljm at ffffffffa0bbe556 [mmfs26]
#16 [ffff883b572afe28] ss_fs_unlocked_ioctl at ffffffffa09b1ac9 [mmfslinux]
#17 [ffff883b572afeb8] do_vfs_ioctl at ffffffff81212235
#18 [ffff883b572aff30] sys_ioctl at ffffffff812124b1
#19 [ffff883b572aff80] system_call_fastpath at ffffffff81696a09