Issue

System panicked due to blocked nfsd tasks with this stack trace:

INFO: task nfsd:23322 blocked for more than 120 seconds.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
nfsd          D 0000000000000005     0 23322      2 0x00000080
 ffff88043869bb90 0000000000000046 0000000000000000 0000000000000000
 ffff880436e0d4c0 0000000000000000 0000000000000000 0000000000000000
 ffff8803fd615ab8 ffff88043869bfd8 000000000000fb88 ffff8803fd615ab8
Call Trace:
 [<ffffffff8150f78e>] __mutex_lock_slowpath+0x13e/0x180
 [<ffffffff8150f62b>] mutex_lock+0x2b/0x50
 [<ffffffffa00af9dd>] ext4_dir_llseek+0x6d/0x1b0 [ext4]
 [<ffffffffa03f37d0>] ? nfsd4_encode_dirent+0x0/0x2d0 [nfsd]
 [<ffffffff8117f90a>] vfs_llseek+0x3a/0x40
 [<ffffffffa03dddbe>] nfsd_readdir+0x6e/0x240 [nfsd]
 [<ffffffffa03f1ea4>] nfsd4_encode_readdir+0x144/0x250 [nfsd]
 [<ffffffffa03ebd35>] nfsd4_encode_operation+0x75/0x180 [nfsd]
 [<ffffffffa03e9d35>] nfsd4_proc_compound+0x195/0x490 [nfsd]
 [<ffffffffa03d743e>] nfsd_dispatch+0xfe/0x240 [nfsd]
 [<ffffffffa03a5614>] svc_process_common+0x344/0x640 [sunrpc]
 [<ffffffff81063410>] ? default_wake_function+0x0/0x20
 [<ffffffffa03a5c50>] svc_process+0x110/0x160 [sunrpc]
 [<ffffffffa03d7b62>] nfsd+0xc2/0x160 [nfsd]
 [<ffffffffa03d7aa0>] ? nfsd+0x0/0x160 [nfsd]
 [<ffffffff81096a36>] kthread+0x96/0xa0
 [<ffffffff8100c0ca>] child_rip+0xa/0x20
 [<ffffffff810969a0>] ? kthread+0x0/0xa0
 [<ffffffff8100c0c0>] ? child_rip+0x0/0x20
Kernel panic - not syncing: hung_task: blocked tasks