zfs 0.6.5.8 hangs during large rsync / high I/O

[danyel2014]

while copying around 5 TB of data between two zpools by using multiple rsync sessions, I've manually started scrub for one of the zpools. Later on I've noticed that any zfs/zpool commands are stalling and my logs are spammed with:

Dec 1 11:06:50 srv_cs1 kernel: INFO: task txg_sync:17368 blocked for more than 120 seconds.
Dec 1 11:06:50 srv_cs1 kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
Dec 1 11:06:50 srv_cs1 kernel: txg_sync D 0000000000000001 0 17368 2 0x00000080
Dec 1 11:06:50 srv_cs1 kernel: ffff885e43b6bac0 0000000000000046 ffff885e41c03980 ffff885e43b6bfd8
Dec 1 11:06:50 srv_cs1 kernel: ffff885e43b6bfd8 ffff885e43b6bfd8 ffff885e41c03980 ffff897eff034780
Dec 1 11:06:50 srv_cs1 kernel: 0000000000000000 7fffffffffffffff ffff887b35ab07a8 0000000000000001
Dec 1 11:06:50 srv_cs1 kernel: Call Trace:
Dec 1 11:06:50 srv_cs1 kernel: [] schedule+0x29/0x70
Dec 1 11:06:50 srv_cs1 kernel: [] schedule_timeout+0x209/0x2d0
Dec 1 11:06:50 srv_cs1 kernel: [] ? default_wake_function+0x12/0x20
Dec 1 11:06:50 srv_cs1 kernel: [] ? __wake_up_common+0x58/0x90
Dec 1 11:06:50 srv_cs1 kernel: [] ? read_tsc+0x9/0x10
Dec 1 11:06:50 srv_cs1 kernel: [] io_schedule_timeout+0xae/0x130
Dec 1 11:06:50 srv_cs1 kernel: [] ? prepare_to_wait_exclusive+0x56/0x90
Dec 1 11:06:50 srv_cs1 kernel: [] io_schedule+0x18/0x20
Dec 1 11:06:50 srv_cs1 kernel: [] cv_wait_common+0xa7/0x130 [spl]
Dec 1 11:06:50 srv_cs1 kernel: [] ? wake_up_atomic_t+0x30/0x30
Dec 1 11:06:50 srv_cs1 kernel: [] __cv_wait_io+0x18/0x20 [spl]
Dec 1 11:06:50 srv_cs1 kernel: [] zio_wait+0x10b/0x1f0 [zfs]
Dec 1 11:06:50 srv_cs1 kernel: [] dsl_pool_sync+0xbf/0x440 [zfs]
Dec 1 11:06:50 srv_cs1 kernel: [] spa_sync+0x388/0xb50 [zfs]
Dec 1 11:06:50 srv_cs1 kernel: [] ? autoremove_wake_function+0x2b/0x40
Dec 1 11:06:50 srv_cs1 kernel: [] txg_sync_thread+0x3c5/0x620 [zfs]
Dec 1 11:06:50 srv_cs1 kernel: [] ? txg_init+0x280/0x280 [zfs]
Dec 1 11:06:50 srv_cs1 kernel: [] thread_generic_wrapper+0x71/0x80 [spl]
Dec 1 11:06:50 srv_cs1 kernel: [] ? __thread_exit+0x20/0x20 [spl]
Dec 1 11:06:50 srv_cs1 kernel: [] kthread+0xcf/0xe0
Dec 1 11:06:50 srv_cs1 kernel: [] ? kthread_create_on_node+0x140/0x140
Dec 1 11:06:50 srv_cs1 kernel: [] ret_from_fork+0x58/0x90
Dec 1 11:06:50 srv_cs1 kernel: [] ? kthread_create_on_node+0x140/0x140
Dec 1 11:10:01 srv_cs1 systemd: Started Session 89 of user root.
Dec 1 11:10:01 srv_cs1 systemd: Starting Session 89 of user root.
Dec 1 11:10:50 srv_cs1 kernel: INFO: task txg_sync:17368 blocked for more than 120 seconds.
Dec 1 11:10:50 srv_cs1 kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
Dec 1 11:10:50 srv_cs1 kernel: txg_sync D 0000000000000001 0 17368 2 0x00000080
Dec 1 11:10:50 srv_cs1 kernel: ffff885e43b6bac0 0000000000000046 ffff885e41c03980 ffff885e43b6bfd8
Dec 1 11:10:50 srv_cs1 kernel: ffff885e43b6bfd8 ffff885e43b6bfd8 ffff885e41c03980 ffff897eff274780
Dec 1 11:10:50 srv_cs1 kernel: 0000000000000000 7fffffffffffffff ffff896381b29058 0000000000000001
Dec 1 11:10:50 srv_cs1 kernel: Call Trace:
Dec 1 11:10:50 srv_cs1 kernel: [] schedule+0x29/0x70
Dec 1 11:10:50 srv_cs1 kernel: [] schedule_timeout+0x209/0x2d0
Dec 1 11:10:50 srv_cs1 kernel: [] ? default_wake_function+0x12/0x20
Dec 1 11:10:50 srv_cs1 kernel: [] ? __wake_up_common+0x58/0x90
Dec 1 11:10:50 srv_cs1 kernel: [] ? read_tsc+0x9/0x10
Dec 1 11:10:50 srv_cs1 kernel: [] io_schedule_timeout+0xae/0x130
Dec 1 11:10:50 srv_cs1 kernel: [] ? prepare_to_wait_exclusive+0x56/0x90
Dec 1 11:10:50 srv_cs1 kernel: [] io_schedule+0x18/0x20
Dec 1 11:10:50 srv_cs1 kernel: [] cv_wait_common+0xa7/0x130 [spl]
Dec 1 11:10:50 srv_cs1 kernel: [] ? wake_up_atomic_t+0x30/0x30
Dec 1 11:10:50 srv_cs1 kernel: [] __cv_wait_io+0x18/0x20 [spl]
Dec 1 11:10:50 srv_cs1 kernel: [] zio_wait+0x10b/0x1f0 [zfs]
Dec 1 11:10:50 srv_cs1 kernel: [] dsl_pool_sync+0xbf/0x440 [zfs]
Dec 1 11:10:50 srv_cs1 kernel: [] spa_sync+0x388/0xb50 [zfs]
Dec 1 11:10:50 srv_cs1 kernel: [] ? autoremove_wake_function+0x2b/0x40
Dec 1 11:10:50 srv_cs1 kernel: [] txg_sync_thread+0x3c5/0x620 [zfs]
Dec 1 11:10:50 srv_cs1 kernel: [] ? txg_init+0x280/0x280 [zfs]
Dec 1 11:10:50 srv_cs1 kernel: [] thread_generic_wrapper+0x71/0x80 [spl]
Dec 1 11:10:50 srv_cs1 kernel: [] ? __thread_exit+0x20/0x20 [spl]
Dec 1 11:10:50 srv_cs1 kernel: [] kthread+0xcf/0xe0
Dec 1 11:10:50 srv_cs1 kernel: [] ? kthread_create_on_node+0x140/0x140
Dec 1 11:10:50 srv_cs1 kernel: [] ret_from_fork+0x58/0x90
Dec 1 11:10:50 srv_cs1 kernel: [] ? kthread_create_on_node+0x140/0x140
Dec 1 11:14:50 srv_cs1 kernel: INFO: task txg_sync:17368 blocked for more than 120 seconds.
Dec 1 11:14:50 srv_cs1 kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
Dec 1 11:14:50 srv_cs1 kernel: txg_sync D 0000000000000001 0 17368 2 0x00000080
Dec 1 11:14:50 srv_cs1 kernel: ffff885e43b6bac0 0000000000000046 ffff885e41c03980 ffff885e43b6bfd8
Dec 1 11:14:50 srv_cs1 kernel: ffff885e43b6bfd8 ffff885e43b6bfd8 ffff885e41c03980 ffff88beffa14780
Dec 1 11:14:50 srv_cs1 kernel: 0000000000000000 7fffffffffffffff ffff8979cad96b90 0000000000000001
Dec 1 11:14:50 srv_cs1 kernel: Call Trace:
Dec 1 11:14:50 srv_cs1 kernel: [] schedule+0x29/0x70
Dec 1 11:14:50 srv_cs1 kernel: [] schedule_timeout+0x209/0x2d0
Dec 1 11:14:50 srv_cs1 kernel: [] ? default_wake_function+0x12/0x20
Dec 1 11:14:50 srv_cs1 kernel: [] ? __wake_up_common+0x58/0x90
Dec 1 11:14:50 srv_cs1 kernel: [] ? read_tsc+0x9/0x10
Dec 1 11:14:50 srv_cs1 kernel: [] io_schedule_timeout+0xae/0x130
Dec 1 11:14:50 srv_cs1 kernel: [] ? prepare_to_wait_exclusive+0x56/0x90
Dec 1 11:14:50 srv_cs1 kernel: [] io_schedule+0x18/0x20
Dec 1 11:14:50 srv_cs1 kernel: [] cv_wait_common+0xa7/0x130 [spl]
Dec 1 11:14:50 srv_cs1 kernel: [] ? wake_up_atomic_t+0x30/0x30
Dec 1 11:14:50 srv_cs1 kernel: [] __cv_wait_io+0x18/0x20 [spl]
Dec 1 11:14:50 srv_cs1 kernel: [] zio_wait+0x10b/0x1f0 [zfs]
Dec 1 11:14:50 srv_cs1 kernel: [] dsl_pool_sync+0xbf/0x440 [zfs]
Dec 1 11:14:50 srv_cs1 kernel: [] spa_sync+0x388/0xb50 [zfs]
Dec 1 11:14:50 srv_cs1 kernel: [] ? autoremove_wake_function+0x2b/0x40
Dec 1 11:14:50 srv_cs1 kernel: [] txg_sync_thread+0x3c5/0x620 [zfs]
Dec 1 11:14:50 srv_cs1 kernel: [] ? txg_init+0x280/0x280 [zfs]
Dec 1 11:14:50 srv_cs1 kernel: [] thread_generic_wrapper+0x71/0x80 [spl]
Dec 1 11:14:50 srv_cs1 kernel: [] ? __thread_exit+0x20/0x20 [spl]
Dec 1 11:14:50 srv_cs1 kernel: [] kthread+0xcf/0xe0
Dec 1 11:14:50 srv_cs1 kernel: [] ? kthread_create_on_node+0x140/0x140
Dec 1 11:14:50 srv_cs1 kernel: [] ret_from_fork+0x58/0x90
Dec 1 11:14:50 srv_cs1 kernel: [] ? kthread_create_on_node+0x140/0x140
Dec 1 11:18:50 srv_cs1 kernel: INFO: task txg_sync:17368 blocked for more than 120 seconds.
Dec 1 11:18:50 srv_cs1 kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
Dec 1 11:18:50 srv_cs1 kernel: txg_sync D 0000000000000001 0 17368 2 0x00000080
Dec 1 11:18:50 srv_cs1 kernel: ffff885e43b6bac0 0000000000000046 ffff885e41c03980 ffff885e43b6bfd8
Dec 1 11:18:50 srv_cs1 kernel: ffff885e43b6bfd8 ffff885e43b6bfd8 ffff885e41c03980 ffff88beffa54780
Dec 1 11:18:50 srv_cs1 kernel: 0000000000000000 7fffffffffffffff ffff8972a73a8c00 0000000000000001
Dec 1 11:18:50 srv_cs1 kernel: Call Trace:
Dec 1 11:18:50 srv_cs1 kernel: [] schedule+0x29/0x70
Dec 1 11:18:50 srv_cs1 kernel: [] schedule_timeout+0x209/0x2d0
Dec 1 11:18:50 srv_cs1 kernel: [] ? default_wake_function+0x12/0x20
Dec 1 11:18:50 srv_cs1 kernel: [] ? __wake_up_common+0x58/0x90
Dec 1 11:18:50 srv_cs1 kernel: [] ? read_tsc+0x9/0x10
Dec 1 11:18:50 srv_cs1 kernel: [] io_schedule_timeout+0xae/0x130
Dec 1 11:18:50 srv_cs1 kernel: [] ? prepare_to_wait_exclusive+0x56/0x90
Dec 1 11:18:50 srv_cs1 kernel: [] io_schedule+0x18/0x20
Dec 1 11:18:50 srv_cs1 kernel: [] cv_wait_common+0xa7/0x130 [spl]
Dec 1 11:18:50 srv_cs1 kernel: [] ? wake_up_atomic_t+0x30/0x30
Dec 1 11:18:50 srv_cs1 kernel: [] __cv_wait_io+0x18/0x20 [spl]
Dec 1 11:18:50 srv_cs1 kernel: [] zio_wait+0x10b/0x1f0 [zfs]
Dec 1 11:18:50 srv_cs1 kernel: [] dsl_pool_sync+0xbf/0x440 [zfs]
Dec 1 11:18:50 srv_cs1 kernel: [] spa_sync+0x388/0xb50 [zfs]
Dec 1 11:18:50 srv_cs1 kernel: [] ? autoremove_wake_function+0x2b/0x40
Dec 1 11:18:50 srv_cs1 kernel: [] txg_sync_thread+0x3c5/0x620 [zfs]
Dec 1 11:18:50 srv_cs1 kernel: [] ? txg_init+0x280/0x280 [zfs]
Dec 1 11:18:50 srv_cs1 kernel: [] thread_generic_wrapper+0x71/0x80 [spl]
Dec 1 11:18:50 srv_cs1 kernel: [] ? __thread_exit+0x20/0x20 [spl]
Dec 1 11:18:50 srv_cs1 kernel: [] kthread+0xcf/0xe0
Dec 1 11:18:50 srv_cs1 kernel: [] ? kthread_create_on_node+0x140/0x140
Dec 1 11:18:50 srv_cs1 kernel: [] ret_from_fork+0x58/0x90
Dec 1 11:18:50 srv_cs1 kernel: [] ? kthread_create_on_node+0x140/0x140
Dec 1 11:20:01 srv_cs1 systemd: Started Session 90 of user root.
Dec 1 11:20:01 srv_cs1 systemd: Starting Session 90 of user root.
Dec 1 11:22:50 srv_cs1 kernel: INFO: task txg_sync:17368 blocked for more than 120 seconds.
Dec 1 11:22:50 srv_cs1 kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
Dec 1 11:22:50 srv_cs1 kernel: txg_sync D 0000000000000001 0 17368 2 0x00000080
Dec 1 11:22:50 srv_cs1 kernel: ffff885e43b6bac0 0000000000000046 ffff885e41c03980 ffff885e43b6bfd8
Dec 1 11:22:50 srv_cs1 kernel: ffff885e43b6bfd8 ffff885e43b6bfd8 ffff885e41c03980 ffff88beff894780
Dec 1 11:22:50 srv_cs1 kernel: 0000000000000000 7fffffffffffffff ffff88c886ca55d8 0000000000000001
Dec 1 11:22:50 srv_cs1 kernel: Call Trace:
Dec 1 11:22:50 srv_cs1 kernel: [] schedule+0x29/0x70
Dec 1 11:22:50 srv_cs1 kernel: [] schedule_timeout+0x209/0x2d0
Dec 1 11:22:50 srv_cs1 kernel: [] ? default_wake_function+0x12/0x20
Dec 1 11:22:50 srv_cs1 kernel: [] ? __wake_up_common+0x58/0x90
Dec 1 11:22:50 srv_cs1 kernel: [] ? read_tsc+0x9/0x10
Dec 1 11:22:50 srv_cs1 kernel: [] io_schedule_timeout+0xae/0x130
Dec 1 11:22:50 srv_cs1 kernel: [] ? prepare_to_wait_exclusive+0x56/0x90
Dec 1 11:22:50 srv_cs1 kernel: [] io_schedule+0x18/0x20
Dec 1 11:22:50 srv_cs1 kernel: [] cv_wait_common+0xa7/0x130 [spl]
Dec 1 11:22:50 srv_cs1 kernel: [] ? wake_up_atomic_t+0x30/0x30
Dec 1 11:22:50 srv_cs1 kernel: [] __cv_wait_io+0x18/0x20 [spl]
Dec 1 11:22:50 srv_cs1 kernel: [] zio_wait+0x10b/0x1f0 [zfs]
Dec 1 11:22:50 srv_cs1 kernel: [] dsl_pool_sync+0xbf/0x440 [zfs]
Dec 1 11:22:50 srv_cs1 kernel: [] spa_sync+0x388/0xb50 [zfs]
Dec 1 11:22:50 srv_cs1 kernel: [] ? autoremove_wake_function+0x2b/0x40
Dec 1 11:22:50 srv_cs1 kernel: [] txg_sync_thread+0x3c5/0x620 [zfs]
Dec 1 11:22:50 srv_cs1 kernel: [] ? txg_init+0x280/0x280 [zfs]
Dec 1 11:22:50 srv_cs1 kernel: [] thread_generic_wrapper+0x71/0x80 [spl]
Dec 1 11:22:50 srv_cs1 kernel: [] ? __thread_exit+0x20/0x20 [spl]
Dec 1 11:22:50 srv_cs1 kernel: [] kthread+0xcf/0xe0
Dec 1 11:22:50 srv_cs1 kernel: [] ? kthread_create_on_node+0x140/0x140
Dec 1 11:22:50 srv_cs1 kernel: [] ret_from_fork+0x58/0x90
Dec 1 11:22:50 srv_cs1 kernel: [] ? kthread_create_on_node+0x140/0x140
Dec 1 11:26:50 srv_cs1 kernel: INFO: task txg_sync:17368 blocked for more than 120 seconds.
Dec 1 11:26:50 srv_cs1 kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
Dec 1 11:26:50 srv_cs1 kernel: txg_sync D 0000000000000001 0 17368 2 0x00000080
Dec 1 11:26:50 srv_cs1 kernel: ffff885e43b6bac0 0000000000000046 ffff885e41c03980 ffff885e43b6bfd8
Dec 1 11:26:50 srv_cs1 kernel: ffff885e43b6bfd8 ffff885e43b6bfd8 ffff885e41c03980 ffff88beffab4780
Dec 1 11:26:50 srv_cs1 kernel: 0000000000000000 7fffffffffffffff ffff8889aba5c478 0000000000000001
Dec 1 11:26:50 srv_cs1 kernel: Call Trace:
Dec 1 11:26:50 srv_cs1 kernel: [] schedule+0x29/0x70
Dec 1 11:26:50 srv_cs1 kernel: [] schedule_timeout+0x209/0x2d0
Dec 1 11:26:50 srv_cs1 kernel: [] ? default_wake_function+0x12/0x20
Dec 1 11:26:50 srv_cs1 kernel: [] ? __wake_up_common+0x58/0x90
Dec 1 11:26:50 srv_cs1 kernel: [] ? read_tsc+0x9/0x10
Dec 1 11:26:50 srv_cs1 kernel: [] io_schedule_timeout+0xae/0x130
Dec 1 11:26:50 srv_cs1 kernel: [] ? prepare_to_wait_exclusive+0x56/0x90
Dec 1 11:26:50 srv_cs1 kernel: [] io_schedule+0x18/0x20
Dec 1 11:26:50 srv_cs1 kernel: [] cv_wait_common+0xa7/0x130 [spl]
Dec 1 11:26:50 srv_cs1 kernel: [] ? wake_up_atomic_t+0x30/0x30
Dec 1 11:26:50 srv_cs1 kernel: [] __cv_wait_io+0x18/0x20 [spl]
Dec 1 11:26:50 srv_cs1 kernel: [] zio_wait+0x10b/0x1f0 [zfs]
Dec 1 11:26:50 srv_cs1 kernel: [] dsl_pool_sync+0xbf/0x440 [zfs]
Dec 1 11:26:50 srv_cs1 kernel: [] spa_sync+0x388/0xb50 [zfs]
Dec 1 11:26:50 srv_cs1 kernel: [] ? autoremove_wake_function+0x2b/0x40
Dec 1 11:26:50 srv_cs1 kernel: [] txg_sync_thread+0x3c5/0x620 [zfs]
Dec 1 11:26:50 srv_cs1 kernel: [] ? txg_init+0x280/0x280 [zfs]
Dec 1 11:26:50 srv_cs1 kernel: [] thread_generic_wrapper+0x71/0x80 [spl]
Dec 1 11:26:50 srv_cs1 kernel: [] ? __thread_exit+0x20/0x20 [spl]
Dec 1 11:26:50 srv_cs1 kernel: [] kthread+0xcf/0xe0
Dec 1 11:26:50 srv_cs1 kernel: [] ? kthread_create_on_node+0x140/0x140
Dec 1 11:26:50 srv_cs1 kernel: [] ret_from_fork+0x58/0x90
Dec 1 11:26:50 srv_cs1 kernel: [] ? kthread_create_on_node+0x140/0x140
Dec 1 11:30:50 srv_cs1 kernel: INFO: task txg_sync:17368 blocked for more than 120 seconds.
Dec 1 11:30:50 srv_cs1 kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
Dec 1 11:30:50 srv_cs1 kernel: txg_sync D 0000000000000001 0 17368 2 0x00000080
Dec 1 11:30:50 srv_cs1 kernel: ffff885e43b6bac0 0000000000000046 ffff885e41c03980 ffff885e43b6bfd8
Dec 1 11:30:50 srv_cs1 kernel: ffff885e43b6bfd8 ffff885e43b6bfd8 ffff885e41c03980 ffff88beff9f4780
Dec 1 11:30:50 srv_cs1 kernel: 0000000000000000 7fffffffffffffff ffff88c8fde6c8d0 0000000000000001
Dec 1 11:30:50 srv_cs1 kernel: Call Trace:
Dec 1 11:30:50 srv_cs1 kernel: [] schedule+0x29/0x70
Dec 1 11:30:50 srv_cs1 kernel: [] schedule_timeout+0x209/0x2d0
Dec 1 11:30:50 srv_cs1 kernel: [] ? default_wake_function+0x12/0x20
Dec 1 11:30:50 srv_cs1 kernel: [] ? __wake_up_common+0x58/0x90
Dec 1 11:30:50 srv_cs1 kernel: [] ? read_tsc+0x9/0x10
Dec 1 11:30:50 srv_cs1 kernel: [] io_schedule_timeout+0xae/0x130
Dec 1 11:30:50 srv_cs1 kernel: [] ? prepare_to_wait_exclusive+0x56/0x90
Dec 1 11:30:50 srv_cs1 kernel: [] io_schedule+0x18/0x20
Dec 1 11:30:50 srv_cs1 kernel: [] cv_wait_common+0xa7/0x130 [spl]
Dec 1 11:30:50 srv_cs1 kernel: [] ? wake_up_atomic_t+0x30/0x30
Dec 1 11:30:50 srv_cs1 kernel: [] __cv_wait_io+0x18/0x20 [spl]
Dec 1 11:30:50 srv_cs1 kernel: [] zio_wait+0x10b/0x1f0 [zfs]
Dec 1 11:30:50 srv_cs1 kernel: [] dsl_pool_sync+0xbf/0x440 [zfs]
Dec 1 11:30:50 srv_cs1 kernel: [] spa_sync+0x388/0xb50 [zfs]
Dec 1 11:30:50 srv_cs1 kernel: [] ? autoremove_wake_function+0x2b/0x40
Dec 1 11:30:50 srv_cs1 kernel: [] txg_sync_thread+0x3c5/0x620 [zfs]
Dec 1 11:30:50 srv_cs1 kernel: [] ? txg_init+0x280/0x280 [zfs]
Dec 1 11:30:50 srv_cs1 kernel: [] thread_generic_wrapper+0x71/0x80 [spl]
Dec 1 11:30:50 srv_cs1 kernel: [] ? __thread_exit+0x20/0x20 [spl]
Dec 1 11:30:50 srv_cs1 kernel: [] kthread+0xcf/0xe0
Dec 1 11:30:50 srv_cs1 kernel: [] ? kthread_create_on_node+0x140/0x140
Dec 1 11:30:50 srv_cs1 kernel: [] ret_from_fork+0x58/0x90
Dec 1 11:30:50 srv_cs1 kernel: [] ? kthread_create_on_node+0x140/0x140
Dec 1 11:34:50 srv_cs1 kernel: INFO: task txg_sync:17368 blocked for more than 120 seconds.
Dec 1 11:34:50 srv_cs1 kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
Dec 1 11:34:50 srv_cs1 kernel: txg_sync D 0000000000000001 0 17368 2 0x00000080
Dec 1 11:34:50 srv_cs1 kernel: ffff885e43b6bac0 0000000000000046 ffff885e41c03980 ffff885e43b6bfd8
Dec 1 11:34:50 srv_cs1 kernel: ffff885e43b6bfd8 ffff885e43b6bfd8 ffff885e41c03980 ffff885eff954780
Dec 1 11:34:50 srv_cs1 kernel: 0000000000000000 7fffffffffffffff ffff88b322117440 0000000000000001
Dec 1 11:34:50 srv_cs1 kernel: Call Trace:
Dec 1 11:34:50 srv_cs1 kernel: [] schedule+0x29/0x70
Dec 1 11:34:50 srv_cs1 kernel: [] schedule_timeout+0x209/0x2d0
Dec 1 11:34:50 srv_cs1 kernel: [] ? default_wake_function+0x12/0x20
Dec 1 11:34:50 srv_cs1 kernel: [] ? __wake_up_common+0x58/0x90
Dec 1 11:34:50 srv_cs1 kernel: [] ? read_tsc+0x9/0x10
Dec 1 11:34:50 srv_cs1 kernel: [] io_schedule_timeout+0xae/0x130
Dec 1 11:34:50 srv_cs1 kernel: [] ? prepare_to_wait_exclusive+0x56/0x90
Dec 1 11:34:50 srv_cs1 kernel: [] io_schedule+0x18/0x20
Dec 1 11:34:50 srv_cs1 kernel: [] cv_wait_common+0xa7/0x130 [spl]
Dec 1 11:34:50 srv_cs1 kernel: [] ? wake_up_atomic_t+0x30/0x30
Dec 1 11:34:50 srv_cs1 kernel: [] __cv_wait_io+0x18/0x20 [spl]
Dec 1 11:34:50 srv_cs1 kernel: [] zio_wait+0x10b/0x1f0 [zfs]
Dec 1 11:34:50 srv_cs1 kernel: [] dsl_pool_sync+0xbf/0x440 [zfs]
Dec 1 11:34:50 srv_cs1 kernel: [] spa_sync+0x388/0xb50 [zfs]
Dec 1 11:34:50 srv_cs1 kernel: [] txg_sync_thread+0x3c5/0x620 [zfs]
Dec 1 11:34:50 srv_cs1 kernel: [] ? txg_init+0x280/0x280 [zfs]
Dec 1 11:34:50 srv_cs1 kernel: [] thread_generic_wrapper+0x71/0x80 [spl]
Dec 1 11:34:50 srv_cs1 kernel: [] ? __thread_exit+0x20/0x20 [spl]
Dec 1 11:34:50 srv_cs1 kernel: [] kthread+0xcf/0xe0
Dec 1 11:34:50 srv_cs1 kernel: [] ? kthread_create_on_node+0x140/0x140
Dec 1 11:34:50 srv_cs1 kernel: [] ret_from_fork+0x58/0x90
Dec 1 11:34:50 srv_cs1 kernel: [] ? kthread_create_on_node+0x140/0x140

I am using RHEL 7.2 with kmod-zfs-0.6.5.8.

[root@srv_cs1 ~]# rpm -qa | grep zfs
zfs-release-1-3.el7.centos.noarch
libzfs2-0.6.5.8-1.el7.centos.x86_64
zfs-0.6.5.8-1.el7.centos.x86_64
kmod-zfs-0.6.5.8-1.el7.centos.x86_64
[root@srv_cs1 ~]# rpm -qa | grep zfs
zfs-release-1-3.el7.centos.noarch
libzfs2-0.6.5.8-1.el7.centos.x86_64
zfs-0.6.5.8-1.el7.centos.x86_64
kmod-zfs-0.6.5.8-1.el7.centos.x86_64

$ uname -a
Linux srv_cs1 3.10.0-327.el7.x86_64 #1 SMP Thu Oct 29 17:29:29 EDT 2015 x86_64 x86_64 x86_64 GNU/Linux