[38420.488067] PM: Syncing filesystems ... done.
[38420.504729] PM: Preparing system for sleep (mem)
[38420.504993] bbswitch: enabling discrete graphics
[38420.665616] Freezing user space processes ... (elapsed 0.002 seconds) done.
[38420.667941] Freezing remaining freezable tasks ... 
[38440.676906] Freezing of tasks failed after 20.008 seconds (1 tasks refusing to freeze, wq_busy=0):
[38440.677009] xfsaild/dm-3    S ffff88041324bdf8     0 24983      2 0x00000000
[38440.677018]  ffff88041324bdf8 0000000000000000 ffff8804adadc9c0 ffff8804137f8000
[38440.677024]  ffff88041324c000 ffff8804137f8000 0000000000000000 ffff8804ad0aef80
[38440.677030]  ffff880399deb800 ffff88041324be10 ffffffff8158eacc 0000000000000000
[38440.677035] Call Trace:
[38440.677050]  [<ffffffff8158eacc>] schedule+0x3c/0x90
[38440.677080]  [<ffffffffa0c13611>] xfsaild+0x631/0x660 [xfs]
[38440.677102]  [<ffffffffa0c12fe0>] ? xfs_trans_ail_cursor_first+0x90/0x90 [xfs]
[38440.677121]  [<ffffffffa0c12fe0>] ? xfs_trans_ail_cursor_first+0x90/0x90 [xfs]
[38440.677128]  [<ffffffff81094c08>] kthread+0xd8/0xf0
[38440.677134]  [<ffffffff81094b30>] ? kthread_worker_fn+0x170/0x170
[38440.677139]  [<ffffffff8159290f>] ret_from_fork+0x3f/0x70
[38440.677144]  [<ffffffff81094b30>] ? kthread_worker_fn+0x170/0x170

[38440.677184] Restarting kernel threads ... done.
[38440.677695] Restarting tasks ... done.
[38440.679442] bbswitch: disabling discrete graphics