Why the pmdtm process is getting blocked for more than 120 seconds ?

Issue

• pmdtm process is getting blocked for more than 120 seconds:

INFO: task pmdtm:21775 blocked for more than 120 seconds.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
pmdtm         D ffff810136437860     0 21775   6464         21779 27293 (NOTLB)
 ffff810311957dc8 0000000000000082 ffff81033a87b448 ffffffff800099ae
 ffff8102896e2860 000000000000000a ffff8102896e2860 ffff810136437860
 00000cdd935664dd 00000000000e1577 ffff8102896e2a48 000000023d826c48
Call Trace:
 [<ffffffff800099ae>] __link_path_walk+0x173/0xf42
 [<ffffffff8002cd2c>] mntput_no_expire+0x19/0x89
 [<ffffffff8000ea75>] link_path_walk+0xa6/0xb2
 [<ffffffff80064c6f>] __mutex_lock_slowpath+0x60/0x9b
 [<ffffffff800236d7>] __path_lookup_intent_open+0x56/0x97
 [<ffffffff80064cb9>] .text.lock.mutex+0xf/0x14
 [<ffffffff8001afe7>] open_namei+0xea/0x6d5
 [<ffffffff80067b88>] do_page_fault+0x4fe/0x874
 [<ffffffff800274fb>] do_filp_open+0x1c/0x38
 [<ffffffff80019e1e>] do_sys_open+0x44/0xbe
 [<ffffffff8005e28d>] tracesys+0xd5/0xe0