Description of problem:
-----------------------

Ganesha crashed while exporting multiple volumes in loop and dumped a core on 3 out of 6 nodes :

Core was generated by `/usr/bin/ganesha.nfsd -L /var/log/ganesha.log -f /etc/ganesha/ganesha.conf -N N'.
Program terminated with signal 11, Segmentation fault.
#0  0x0000562c8dd15ea3 in mdc_up_invalidate (export=0x7fab1cf352e0, handle=0x7fa884002858, flags=271) at /usr/src/debug/nfs-ganesha-2.4.4/src/FSAL/Stackable_FSALs/FSAL_MDCACHE/mdcache_up.c:55
55		key.fsal = export->sub_export->fsal;
(gdb) bt
#0  0x0000562c8dd15ea3 in mdc_up_invalidate (export=0x7fab1cf352e0, handle=0x7fa884002858, flags=271) at /usr/src/debug/nfs-ganesha-2.4.4/src/FSAL/Stackable_FSALs/FSAL_MDCACHE/mdcache_up.c:55
#1  0x0000562c8dc55fe9 in queue_invalidate (ctx=<optimized out>) at /usr/src/debug/nfs-ganesha-2.4.4/src/FSAL_UP/fsal_up_async.c:81
#2  0x0000562c8dcf3889 in fridgethr_start_routine (arg=0x7fa9480019e0) at /usr/src/debug/nfs-ganesha-2.4.4/src/support/fridgethr.c:550
#3  0x00007fabab11fe25 in start_thread (arg=0x7fa80ce3b700) at pthread_create.c:308
#4  0x00007fabaa7ed34d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:113
(gdb) 


Version-Release number of selected component (if applicable):
-------------------------------------------------------------

glusterfs-ganesha-3.8.4-50.el7rhgs.x86_64
nfs-ganesha-2.4.4-17.el7rhgs.x86_64


How reproducible:
-----------------

1/1 , but same crash on 3 nodes.