zfs hangs by a ls in snapshot dir created by mkdir

[ 2121.900985] INFO: task ls:7557 blocked for more than 120 seconds.
[ 2122.196911] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 2122.577276] ls              D ffff881fffbd3680     0  7557   7081 0x00000084
[ 2122.919648]  ffff881fbc023bb0 0000000000000086 ffff881fc6ac8b60 ffff881fbc023fd8
[ 2123.278971]  ffff881fbc023fd8 ffff881fbc023fd8 ffff881fc6ac8b60 ffffffffa029f520
[ 2123.638320]  ffffffffa029f524 ffff881fc6ac8b60 00000000ffffffff ffffffffa029f528
[ 2123.998210] Call Trace:
[ 2124.116623]  [<ffffffff8160aac9>] schedule_preempt_disabled+0x29/0x70
[ 2124.429350]  [<ffffffff81608815>] __mutex_lock_slowpath+0xc5/0x1c0
[ 2124.729387]  [<ffffffff8126945c>] ? security_inode_permission+0x1c/0x30
[ 2125.050751]  [<ffffffff81607c7f>] mutex_lock+0x1f/0x2f
[ 2125.300407]  [<ffffffffa013ee16>] zfsctl_snapshot_unmount_delay+0x26/0xa0 [zfs]
[ 2125.655334]  [<ffffffffa0174227>] zpl_revalidate+0xb7/0x110 [zfs]
[ 2125.951393]  [<ffffffff811d1964>] lookup_fast+0x294/0x2e0
[ 2126.214219]  [<ffffffff811d4865>] path_lookupat+0x165/0x7a0
[ 2126.485868]  [<ffffffff81156ceb>] ? unlock_page+0x2b/0x30
[ 2126.749209]  [<ffffffff8117e981>] ? __do_fault+0x401/0x510
[ 2127.016250]  [<ffffffff811ab915>] ? kmem_cache_alloc+0x35/0x1d0
[ 2127.304706]  [<ffffffff811d6ddf>] ? getname_flags+0x4f/0x1a0
[ 2127.581018]  [<ffffffff811d4ecb>] filename_lookup+0x2b/0xc0
[ 2127.853434]  [<ffffffff811d7f07>] user_path_at_empty+0x67/0xc0
[ 2128.137684]  [<ffffffff8160f914>] ? __do_page_fault+0x204/0x520
[ 2128.426566]  [<ffffffff811d7f71>] user_path_at+0x11/0x20
[ 2128.685198]  [<ffffffff811cb8e3>] vfs_fstatat+0x63/0xc0
[ 2128.940603]  [<ffffffff811da490>] ? fillonedir+0xe0/0xe0
[ 2129.199604]  [<ffffffff811cbeb1>] SYSC_newlstat+0x31/0x60
[ 2129.462255]  [<ffffffff8160fc4a>] ? do_page_fault+0x1a/0x70
[ 2129.733650]  [<ffffffff8160be88>] ? page_fault+0x28/0x30
[ 2129.992830]  [<ffffffff811cc13e>] SyS_newlstat+0xe/0x10
[ 2130.247548]  [<ffffffff81614409>] system_call_fastpath+0x16/0x1b