The
1) mclbytes = 2048
2) nmbclusters(number of clusters) = 8192 

when I try to allocate/get mbuf cluster greater than 8192 io-pkt hangs instead of returning NULL.
the code looks to take mbuf looks like 

wtp = WTP
m = m_getcl_wtp (M_DONTWAIT, MT_DATA, M_PKTHDR, wtp);


The wtp is assigned to WTP present in siglock.h
#define WTP (stk_ctl.work_threads[NW_TID_TO_TIDX(LIBC_TLS_TID())])

Is there precondition or setting needs to be done to prevent this behaviour?
io-pkt is already up and running.
I am mounting my driver using "mount" command.

There is also a devnp-e1000.so running but it does not have any issues.
Looking forward for reply.

Thank you.