Task blocked, traces in syslog

[aikudinov]

Got this in syslog: http://pastebin.ca/3304890
Ubuntu 15.10, swap on zvol

[3725092.918403] INFO: task dpkg:10163 blocked for more than 120 seconds.
[3725092.918407] Tainted: P OE 4.2.0-19-generic #23-Ubuntu
[3725092.918408] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[3725092.918409] dpkg D ffff88041fc96640 0 10163 5700 0x00000000
[3725092.918412] ffff88005bc87248 0000000000000086 ffff88040d68a580 ffff8800c8adf080
[3725092.918414] ffff88005bc87278 ffff88005bc88000 ffff880035169424 ffff8800c8adf080
[3725092.918415] 00000000ffffffff ffff880035169428 ffff88005bc87268 ffffffff817ec197
[3725092.918416] Call Trace:
[3725092.918424] [] schedule+0x37/0x80
[3725092.918426] [] schedule_preempt_disabled+0xe/0x10
[3725092.918428] [] __mutex_lock_slowpath+0xb5/0x120
[3725092.918429] [] mutex_lock+0x23/0x40
[3725092.918464] [] zfs_zinactive+0x56/0x1a0 [zfs]
[3725092.918485] [] zfs_inactive+0x61/0x270 [zfs]
[3725092.918488] [] ? truncate_pagecache+0x5e/0x70
[3725092.918508] [] zpl_evict_inode+0x47/0x60 [zfs]
[3725092.918511] [] evict+0xba/0x180
[3725092.918512] [] dispose_list+0x3a/0x50
[3725092.918513] [] prune_icache_sb+0x5a/0x80
[3725092.918516] [] super_cache_scan+0x14f/0x1a0
[3725092.918518] [] shrink_slab+0x20e/0x3b0
[3725092.918520] [] shrink_zone+0x2b9/0x2d0
[3725092.918521] [] do_try_to_free_pages+0x16d/0x400
[3725092.918523] [] try_to_free_pages+0x10a/0x150
[3725092.918525] [] __alloc_pages_nodemask+0x5eb/0xa10
[3725092.918527] [] alloc_pages_current+0x91/0x100
[3725092.918529] [] new_slab+0x368/0x450
[3725092.918530] [] __slab_alloc+0x27f/0x4b0
[3725092.918534] [] ? spl_kmem_zalloc+0xa3/0x180 [spl]
[3725092.918536] [] ? mutex_lock+0x16/0x40
[3725092.918545] [] ? dbuf_read+0x66d/0x860 [zfs]
[3725092.918547] [] ? mutex_lock+0x16/0x40
[3725092.918548] [] __kmalloc_node+0xb5/0x2e0
[3725092.918551] [] spl_kmem_zalloc+0xa3/0x180 [spl]
[3725092.918560] [] dbuf_hold_impl+0x41/0xa0 [zfs]
[3725092.918570] [] dbuf_hold+0x2f/0x60 [zfs]
[3725092.918583] [] dnode_hold_impl+0x85/0x4e0 [zfs]
[3725092.918586] [] ? spl_kmem_cache_alloc+0x72/0x7e0 [spl]
[3725092.918598] [] dnode_hold+0x19/0x20 [zfs]
[3725092.918609] [] dmu_bonus_hold+0x36/0x280 [zfs]
[3725092.918626] [] sa_buf_hold+0xe/0x10 [zfs]
[3725092.918646] [] zfs_zget+0x1b4/0x330 [zfs]
[3725092.918666] [] ? zio_rewrite+0x64/0x70 [zfs]
[3725092.918686] [] ? zil_add_block+0x190/0x190 [zfs]
[3725092.918707] [] zfs_get_data+0x63/0x2f0 [zfs]
[3725092.918727] [] ? zil_add_block+0x190/0x190 [zfs]
[3725092.918747] [] ? zpl_write_common_iovec+0xe0/0xe0 [zfs]
[3725092.918767] [] zil_commit.part.11+0x62e/0x7e0 [zfs]
[3725092.918787] [] zil_commit+0x17/0x20 [zfs]
[3725092.918810] [] zpl_writepages+0xd9/0x170 [zfs]
[3725092.918812] [] do_writepages+0x1e/0x30
[3725092.918814] [] __filemap_fdatawrite_range+0xcc/0x100
[3725092.918816] [] filemap_fdatawrite_range+0x13/0x20
[3725092.918818] [] SyS_sync_file_range+0x145/0x160
[3725092.918820] [] entry_SYSCALL_64_fastpath+0x16/0x75

[behlendorf]

This looks like a duplicate of #4106, there is a fix in #4124 currently under review.