nfs server crashed due to assert since the read_child was -1. Setup:

2 replica setup

1 fuse client executing sanity script
1 nfs client executing sanity script

volume set operations in a loop
brick kill, sleep and bring brick up

find | xargs stat on fuse mount point.

nfs server crashed with the following backtrace.

Core was generated by `/usr/local/sbin/glusterfs -f /etc/glusterd/nfs/nfs-server.vol -p /etc/glusterd/'.
Program terminated with signal 6, Aborted.
#0  0x0000003eb5e30265 in raise () from /lib64/libc.so.6
(gdb) bt
#0  0x0000003eb5e30265 in raise () from /lib64/libc.so.6
#1  0x0000003eb5e31d10 in abort () from /lib64/libc.so.6
#2  0x0000003eb5e296e6 in __assert_fail () from /lib64/libc.so.6
#3  0x00002aaaaad0f3f1 in afr_transaction_rm_stale_children (frame=0x2ad8a0c430d4, this=0x64b34c0, inode=0x2aaaabcdf2dc, 
    type=AFR_DATA_TRANSACTION) at ../../../../../xlators/cluster/afr/src/afr-transaction.c:414
#4  0x00002aaaaad0f625 in afr_changelog_post_op (frame=0x2ad8a0c430d4, this=0x64b34c0)
    at ../../../../../xlators/cluster/afr/src/afr-transaction.c:492
#5  0x00002aaaaad135e8 in afr_transaction_resume (frame=0x2ad8a0c430d4, this=0x64b34c0)
    at ../../../../../xlators/cluster/afr/src/afr-transaction.c:1187
#6  0x00002aaaaad045ca in afr_writev_wind_cbk (frame=0x2ad8a0c430d4, cookie=0x1, this=0x64b34c0, op_ret=65536, op_errno=0, 
    prebuf=0x7fff175596d0, postbuf=0x7fff17559660) at ../../../../../xlators/cluster/afr/src/afr-inode-write.c:124
#7  0x00002aaaaaac20d3 in client3_1_writev_cbk (req=0x2aaaad72a04c, iov=0x2aaaad72a08c, count=1, myframe=0x2ad8a09920f8)
    at ../../../../../xlators/protocol/client/src/client3_1-fops.c:692
#8  0x00002ad89fd0125e in rpc_clnt_handle_reply (clnt=0x64c6ec0, pollin=0x64d4bb0) at ../../../../rpc/rpc-lib/src/rpc-clnt.c:789
#9  0x00002ad89fd01586 in rpc_clnt_notify (trans=0x64c71f0, mydata=0x64c6ef0, event=RPC_TRANSPORT_MSG_RECEIVED, data=0x64d4bb0)
    at ../../../../rpc/rpc-lib/src/rpc-clnt.c:902
#10 0x00002ad89fcfd9f3 in rpc_transport_notify (this=0x64c71f0, event=RPC_TRANSPORT_MSG_RECEIVED, data=0x64d4bb0)
    at ../../../../rpc/rpc-lib/src/rpc-transport.c:498
#11 0x00002aaaad4daea7 in socket_event_poll_in (this=0x64c71f0) at ../../../../../rpc/rpc-transport/socket/src/socket.c:1675
#12 0x00002aaaad4db3e9 in socket_event_handler (fd=10, idx=4, data=0x64c71f0, poll_in=1, poll_out=0, poll_err=0)
    at ../../../../../rpc/rpc-transport/socket/src/socket.c:1790
#13 0x00002ad89faa984c in event_dispatch_epoll_handler (event_pool=0x64ab960, events=0x64c9e30, i=0)
    at ../../../libglusterfs/src/event.c:794
#14 0x00002ad89faa9a51 in event_dispatch_epoll (event_pool=0x64ab960) at ../../../libglusterfs/src/event.c:856
#15 0x00002ad89faa9dab in event_dispatch (event_pool=0x64ab960) at ../../../libglusterfs/src/event.c:956
#16 0x000000000040784d in main (argc=7, argv=0x7fff17559d68) at ../../../glusterfsd/src/glusterfsd.c:1592
(gdb) f 3
#3  0x00002aaaaad0f3f1 in afr_transaction_rm_stale_children (frame=0x2ad8a0c430d4, this=0x64b34c0, inode=0x2aaaabcdf2dc, 
    type=AFR_DATA_TRANSACTION) at ../../../../../xlators/cluster/afr/src/afr-transaction.c:414
414                     GF_ASSERT (read_child >= 0);
(gdb) p read_child
$1 = -1
(gdb) f 4
#4  0x00002aaaaad0f625 in afr_changelog_post_op (frame=0x2ad8a0c430d4, this=0x64b34c0)
    at ../../../../../xlators/cluster/afr/src/afr-transaction.c:492
492                     afr_transaction_rm_stale_children (frame, this,
(gdb) l
487
488             __mark_down_children (local->pending, priv->child_count,
489                                   local->child_up, local->transaction.type);
490
491             if (local->fd)
492                     afr_transaction_rm_stale_children (frame, this,
493                                                        local->fd->inode,
494                                                        local->transaction.type);
495
496             xattr = alloca (priv->child_count * sizeof (*xattr));
(gdb) (gdb) 
375             afr_local_t     *local = NULL;
376             int             **pending = NULL;
377             int             idx = 0;
378             int32_t         *stale_children = NULL;
379             int32_t         *fresh_children = NULL;
380             gf_boolean_t    rm_stale_children = _gf_false;
381
382             idx = afr_index_for_transaction_type (type);
383
384             priv = this->private;
(gdb) 
385             local = frame->local;
386             pending = local->pending;
387
388             stale_children = afr_children_create (priv->child_count);
389             if (!stale_children)
390                     goto out;
391
392             fresh_children = local->fresh_children;
393             read_child = afr_inode_get_read_ctx (this, inode, fresh_children);
394
(gdb) 
395             GF_ASSERT (read_child >= 0);
396
397             if (pending[read_child][idx] == 0)
398                     read_child = -1;
399
400             for (i = 0; i < priv->child_count; i++) {
401                     if (!afr_is_child_present (fresh_children,
402                                                priv->child_count, i))
403                             continue;
404                     if (pending[i][idx] == 0) {
(gdb) p fresh_children[0]
$2 = -1
(gdb) p fresh_children[1]
$3 = -1
(gdb)