Index: uspace/lib/c/arch/amd64/include/elf_linux.h
===================================================================
--- uspace/lib/c/arch/amd64/include/elf_linux.h	(revision 71450c851fb728ac6d9a6f1118949d81152b67e9)
+++ uspace/lib/c/arch/amd64/include/elf_linux.h	(revision 05f5fbfc5c9c4326cfcfe05020160cd425e78353)
@@ -66,4 +66,16 @@
 	uint64_t rsp;
 	uint64_t ss;
+
+	/*
+	 * The following registers need to be part of elf_regs_t.
+	 * Unfortunately, we don't have any information about them in our
+	 * istate_t.
+	 */
+	uint64_t unused_fs_base;
+	uint64_t unused_gs_base;
+	uint64_t unused_ds;
+	uint64_t unused_es;
+	uint64_t unused_fs;
+	uint64_t unused_gs;
 } elf_regs_t;
 
@@ -91,4 +103,14 @@
 	elf_regs->rsp = istate->rsp;
 	elf_regs->ss = istate->ss;
+
+	/*
+	 * Reset the registers for which there is not enough info in istate_t.
+	 */
+	elf_regs->unused_fs_base = 0;
+	elf_regs->unused_gs_base = 0;
+	elf_regs->unused_ds = 0;
+	elf_regs->unused_es = 0;
+	elf_regs->unused_fs = 0;
+	elf_regs->unused_gs = 0;
 }
 
Index: uspace/srv/net/tcp/sock.c
===================================================================
--- uspace/srv/net/tcp/sock.c	(revision 71450c851fb728ac6d9a6f1118949d81152b67e9)
+++ uspace/srv/net/tcp/sock.c	(revision 05f5fbfc5c9c4326cfcfe05020160cd425e78353)
@@ -779,4 +779,9 @@
 	}
 
+	/* Grab recv_buffer_lock because of CV wait in tcp_sock_recv_fibril() */
+	fibril_mutex_lock(&socket->recv_buffer_lock);
+	socket->sock_core = NULL;
+	fibril_mutex_unlock(&socket->recv_buffer_lock);
+
 	rc = socket_destroy(NULL, socket_id, &client->sockets, &gsock,
 	    tcp_free_sock_data);
@@ -839,8 +844,9 @@
 	log_msg(LVL_DEBUG, "tcp_sock_recv_fibril()");
 
+	fibril_mutex_lock(&sock->recv_buffer_lock);
+
 	while (true) {
 		log_msg(LVL_DEBUG, "call tcp_uc_receive()");
-		fibril_mutex_lock(&sock->recv_buffer_lock);
-		while (sock->recv_buffer_used != 0)
+		while (sock->recv_buffer_used != 0 && sock->sock_core != NULL)
 			fibril_condvar_wait(&sock->recv_buffer_cv,
 			    &sock->recv_buffer_lock);
@@ -852,6 +858,6 @@
 			sock->recv_error = trc;
 			fibril_condvar_broadcast(&sock->recv_buffer_cv);
-			fibril_mutex_unlock(&sock->recv_buffer_lock);
-			tcp_sock_notify_data(sock->sock_core);
+			if (sock->sock_core != NULL)
+				tcp_sock_notify_data(sock->sock_core);
 			break;
 		}
@@ -861,7 +867,9 @@
 		sock->recv_buffer_used = data_len;
 		fibril_condvar_broadcast(&sock->recv_buffer_cv);
-		fibril_mutex_unlock(&sock->recv_buffer_lock);
-		tcp_sock_notify_data(sock->sock_core);
-	}
+		if (sock->sock_core != NULL)
+			tcp_sock_notify_data(sock->sock_core);
+	}
+
+	fibril_mutex_unlock(&sock->recv_buffer_lock);
 
 	tcp_uc_delete(sock->conn);