Description of problem:
Mount NFS share on two clients. Created random files with different sizes in 10*10 directory structure. After creating about 46K files, started renaming files at the top level. Started hitting Input/Output error while renaming.

Version-Release number of selected component (if applicable):
ceph-radosgw-10.2.5-3.el7cp.x86_64

Steps to Reproduce:
1. Configure nfs-ganesha on RGW server and create an S3 bucket. Mount export on two clients.
2. Start creating random size files with -b 10 -d 10 -n 1000 where n is number of files that created at each directory level.  
3. Also, parallely start running S3 workload of creating objects on the same bucket 'my-new-bucket'. 
4. It was working fine until this point. About 46K files were created and both S3 ops and file ops were OK.
5. Now on another mountpoint, start renaming files from top. During this process, an I/O error occured and ls command were hung. 
6. nfsd process had exited with segfault:

    -2> 2017-01-18 09:01:42.399707 7f6b2a7f4700  2 req 0:0.937762:: :list_bucket:http status=200
    -1> 2017-01-18 09:01:42.399712 7f6b2a7f4700  1 ====== process_request req done req=0x7f6b2a7f2a30 http_status=200 ======
     0> 2017-01-18 09:01:42.401168 7f6adb756700 -1 *** Caught signal (Segmentation fault) **
 in thread 7f6adb756700 thread_name:ganesha.nfsd

 ceph version 10.2.5-3.el7cp (1337a819287fd59af47dbbe186c465dfa1b384e7)
 1: (()+0x56e10a) [0x7f6c617a610a]
 2: (()+0xf370) [0x7f6c6dffb370]
 3: (mdcache_dirent_rename()+0x1b7) [0x7f6c6fb41137]
 4: (()+0x10628a) [0x7f6c6fb3728a]
 5: (fsal_rename()+0x169) [0x7f6c6fa70099]
 6: (nfs4_op_rename()+0x192) [0x7f6c6faab6c2]
 7: (nfs4_Compound()+0x63d) [0x7f6c6fa96fcd]
 8: (nfs_rpc_execute()+0x5bc) [0x7f6c6fa8817c]
 9: (()+0x587da) [0x7f6c6fa897da]
 10: (()+0xe2459) [0x7f6c6fb13459]
 11: (()+0x7dc5) [0x7f6c6dff3dc5]
 12: (clone()+0x6d) [0x7f6c6d6c273d]