Description of problem:
(gdb) bt full
#0  0x00000032f1e32885 in raise () from /lib64/libc.so.6
No symbol table info available.
#1  0x00000032f1e34065 in abort () from /lib64/libc.so.6
No symbol table info available.
#2  0x00000032f1e2b9fe in __assert_fail_base () from /lib64/libc.so.6
No symbol table info available.
#3  0x00000032f1e2bac0 in __assert_fail () from /lib64/libc.so.6
No symbol table info available.
#4  0x00007fe315a0e6ab in __gf_free (free_ptr=0x1443400) at mem-pool.c:278
        req_size = 0
        ptr = 0x14433f4 ""
        type = 0
        xl = 0x0
        __PRETTY_FUNCTION__ = "__gf_free"
#5  0x00007fe310ff32e3 in gf_defrag_start_crawl (data=0x1425b00) at dht-rebalance.c:1485
        this = 0x1425b00
        conf = 0x14432f0
        defrag = 0x1443400
        ret = -1
        loc = {path = 0x7fe311032eaf "/", name = 0x0, inode = 0x7fe2d161a04c, parent = 0x0, gfid = '\000' <repeats 15 times>, "\001", 
          pargfid = '\000' <repeats 15 times>}
        iatt = {ia_ino = 0, ia_gfid = '\000' <repeats 15 times>, ia_dev = 0, ia_type = IA_INVAL, ia_prot = {suid = 0 '\000', sgid = 0 '\000', sticky = 0 '\000', 
            owner = {read = 0 '\000', write = 0 '\000', exec = 0 '\000'}, group = {read = 0 '\000', write = 0 '\000', exec = 0 '\000'}, other = {read = 0 '\000', 
              write = 0 '\000', exec = 0 '\000'}}, ia_nlink = 0, ia_uid = 0, ia_gid = 0, ia_rdev = 0, ia_size = 0, ia_blksize = 0, ia_blocks = 0, ia_atime = 0, 
          ia_atime_nsec = 0, ia_mtime = 0, ia_mtime_nsec = 0, ia_ctime = 0, ia_ctime_nsec = 0}
        parent = {ia_ino = 0, ia_gfid = '\000' <repeats 15 times>, ia_dev = 0, ia_type = IA_INVAL, ia_prot = {suid = 0 '\000', sgid = 0 '\000', sticky = 0 '\000', 
            owner = {read = 0 '\000', write = 0 '\000', exec = 0 '\000'}, group = {read = 0 '\000', write = 0 '\000', exec = 0 '\000'}, other = {read = 0 '\000', 
              write = 0 '\000', exec = 0 '\000'}}, ia_nlink = 0, ia_uid = 0, ia_gid = 0, ia_rdev = 0, ia_size = 0, ia_blksize = 0, ia_blocks = 0, ia_atime = 0, 
          ia_atime_nsec = 0, ia_mtime = 0, ia_mtime_nsec = 0, ia_ctime = 0, ia_ctime_nsec = 0}
        fix_layout = 0x0
        migrate_data = 0x0
        __FUNCTION__ = "gf_defrag_start_crawl"
#6  0x00007fe315a1f286 in synctask_wrap (old_task=0x7fe2c8200d70) at syncop.c:128
        task = 0x7fe2c8200d70
#7  0x00000032f1e43610 in ?? () from /lib64/libc.so.6
No symbol table info available.


Version-Release number of selected component (if applicable):
3.3.0qa33

gfsc1.sh:-
-----------
#!/bin/bash

mountpoint=`pwd`
for i in {1..10}
do
	level1_dir=$mountpoint/fuse2.$i
	mkdir $level1_dir
	cd $level1_dir
	for j in {1..20}
	do 
		level2_dir=dir.$j
		mkdir $level2_dir
		cd $level2_dir
		for k in {1..100}
		do 
			echo "Creating File: $leve1_dir/$level2_dir/file.$k"
			dd if=/dev/zero of=file.$k bs=1M count=$k 
		done
		cd $level1_dir
	done
	cd $mountpoint
done


nfsc1.sh:-
----------
#!/bin/bash

mountpoint=`pwd`
for i in {1..5}
do 
	level1_dir=$mountpoint/nfs2.$i
	mkdir $level1_dir
	cd $level1_dir
	for j in {1..20}
	do 
		level2_dir=dir.$j
		mkdir $level2_dir
		cd $level2_dir

		for k in {1..100}
		do 
			echo "Creating File: $leve1_dir/$level2_dir/file.$k"
			dd if=/dev/zero of=file.$k bs=1M count=$k
		
		done
		cd $level1_dir
	done
	cd $mountpoint
done

Steps to Reproduce:
1.create distribute-replicate volume(2X3). start the volume.
2.create fuse, nfs mounts. 
3.run gfsc1.sh from fuse mount
4.run nfsc1.sh from nfs mount
4.add-brick to the volume
5.start rebalance 
6.status rebalance
7.stop rebalance
8.brink down 2 bricks from each replicate set, so that one brick is online from each replica set
9.brick back bricks online
10.start force rebalance
11.query rebalance status 
12.stop rebalance

Repeat step8 to step12 3-4 times. 

Actual results:
rebalance process crashed.