Description of problem:
(gdb) bt
#0  0x00007f2758899c62 in list_del_init (old=0x7f273c020ed0) at ../../../../../libglusterfs/src/list.h:71
#1  0x00007f275889b1c8 in __delete_lock (pl_inode=0x7f273c00ac30, lock=0x7f273c020ed0)
    at ../../../../../xlators/features/locks/src/common.c:516
#2  0x00007f275889c196 in __insert_and_merge (pl_inode=0x7f273c00ac30, lock=0x7f273c020ed0)
    at ../../../../../xlators/features/locks/src/common.c:820
#3  0x00007f275889c094 in __insert_and_merge (pl_inode=0x7f273c00ac30, lock=0x7f273c0339e0)
    at ../../../../../xlators/features/locks/src/common.c:803
#4  0x00007f275889cd8a in pl_setlk (this=0x1f888a0, pl_inode=0x7f273c00ac30, lock=0x7f273c0339e0, can_block=0)
    at ../../../../../xlators/features/locks/src/common.c:1027
#5  0x00007f27588a314c in pl_lk (frame=0x7f275b80b7f8, this=0x1f888a0, fd=0x1fb9190, cmd=6, flock=0x7f275b4c26fc, xdata=0x0)
    at ../../../../../xlators/features/locks/src/posix.c:1229
#6  0x00007f27586871ab in iot_lk_wrapper (frame=0x7f275b80008c, this=0x1f89a20, fd=0x1fb9190, cmd=6, flock=0x7f275b4c26fc, 
    xdata=0x0) at ../../../../../xlators/performance/io-threads/src/io-threads.c:1137
#7  0x00007f275c9e8fe0 in call_resume_wind (stub=0x7f275b4c26ac) at ../../../libglusterfs/src/call-stub.c:2640
#8  0x00007f275c9f067a in call_resume (stub=0x7f275b4c26ac) at ../../../libglusterfs/src/call-stub.c:4160
#9  0x00007f27586808cf in iot_worker (data=0x1fa0620) at ../../../../../xlators/performance/io-threads/src/io-threads.c:138
#10 0x0000003680c07b41 in start_thread () from /lib64/libpthread.so.0
#11 0x00000036808df49d in clone () from /lib64/libc.so.6

(gdb) info thr
  Id   Target Id         Frame 
  10   Thread 0x7f275b334700 (LWP 8731) 0x0000003680c0ec27 in do_sigwait () from /lib64/libpthread.so.0
  9    Thread 0x7f2752fc2700 (LWP 8812) 0x0000003680c0b82f in pthread_cond_timedwait@@GLIBC_2.3.2 ()
   from /lib64/libpthread.so.0
  8    Thread 0x7f275c54c720 (LWP 8730) 0x00000036808dfa73 in epoll_wait () from /lib64/libc.so.6
  7    Thread 0x7f275359f700 (LWP 8738) 0x0000003680c0b82f in pthread_cond_timedwait@@GLIBC_2.3.2 ()
   from /lib64/libpthread.so.0
  6    Thread 0x7f274bfff700 (LWP 8740) 0x0000003680c0b82f in pthread_cond_timedwait@@GLIBC_2.3.2 ()
   from /lib64/libpthread.so.0
  5    Thread 0x7f27536a0700 (LWP 8737) 0x0000003680c0b4c5 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
  4    Thread 0x7f27596ef700 (LWP 8736) 0x0000003680c0e75d in nanosleep () from /lib64/libpthread.so.0
  3    Thread 0x7f275a332700 (LWP 8733) 0x0000003680c0b4c5 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
  2    Thread 0x7f275ab33700 (LWP 8732) 0x0000003680c0b4c5 in pthread_cond_wait@@GLIBC_2.3.2 () from /lib64/libpthread.so.0
* 1    Thread 0x7f2752ec1700 (LWP 8814) 0x00007f2758899c62 in list_del_init (old=0x7f273c020ed0)
    at ../../../../../libglusterfs/src/list.h:71

(gdb) up
#1  0x00007f275889b1c8 in __delete_lock (pl_inode=0x7f273c00ac30, lock=0x7f273c020ed0)
    at ../../../../../xlators/features/locks/src/common.c:516
516	        list_del_init (&lock->list);
(gdb) p *lock
$1 = {list = {next = 0x0, prev = 0x0}, fl_type = 1, fl_start = 0, fl_end = 9223372036854775807, blocked = 0, user_flock = {
    l_type = 0, l_whence = 0, l_start = 0, l_len = 0, l_pid = 0, l_owner = {len = 0, data = '\000' <repeats 1023 times>}}, 
  this = 0x0, fd_num = 33264016, fd = 0x0, frame = 0x0, blkd_time = {tv_sec = 0, tv_usec = 0}, granted_time = {tv_sec = 0, 
    tv_usec = 0}, transport = 0x1face60, owner = {len = 8, data = "\036\216C\\Vi\347\027", '\000' <repeats 1015 times>}, 
  client_pid = 10265}
(gdb) up
#2  0x00007f275889c196 in __insert_and_merge (pl_inode=0x7f273c00ac30, lock=0x7f273c020ed0)
    at ../../../../../xlators/features/locks/src/common.c:820
820	                                __delete_lock (pl_inode, lock);
(gdb) p *pl_inode
$2 = {mutex = {__data = {__lock = 1, __count = 0, __owner = 8814, __nusers = 1, __kind = 0, __spins = 0, __list = {
        __prev = 0x0, __next = 0x0}}, 
    __size = "\001\000\000\000\000\000\000\000n\"\000\000\001", '\000' <repeats 26 times>, __align = 1}, dom_list = {
    next = 0x7f27380497e0, prev = 0x7f273c00ad00}, ext_list = {next = 0x7f273c025e20, prev = 0x7f273c025e20}, rw_list = {
    next = 0x7f273c00ac78, prev = 0x7f273c00ac78}, reservelk_list = {next = 0x7f273c00ac88, prev = 0x7f273c00ac88}, 
  blocked_reservelks = {next = 0x7f273c00ac98, prev = 0x7f273c00ac98}, blocked_calls = {next = 0x7f273c00aca8, 
    prev = 0x7f273c00aca8}, mandatory = 0, refkeeper = 0x7f2753277640}
(gdb) 


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


How reproducible: happened 2/3


Additional info:
Volume Name: a
Type: Distributed-Replicate
Volume ID: 9e1f5ab2-e363-4395-bb62-37b32db8c58f
Status: Started
Number of Bricks: 2 x 2 = 4
Transport-type: tcp
Bricks:
Brick1: supernova:/tmp/export/a1
Brick2: supernova:/tmp/export/a2
Brick3: supernova:/tmp/export/a3
Brick4: supernova:/tmp/export/a4
Options Reconfigured:
geo-replication.indexing: on
features.quota: on