staging/lustre/ptlrpc: Race between start and stop service threads

When ptlrpc_start_thread fails to create a new thread, it will
finalize and free a struct ptlrpc_thread created and used here.
Considering this, it can be a problem when ptlrpc_svcpt_stop_thread
is driven and handles the struct ptlrpc_thread right after or right
before failure of cfs_create_thread. Because this situation let
the both of ptlrpc_start_thread and ptlrpc_svcpt_stop_threads
access the freed ptlrpc_thread and cause OS panic. Or, it may
happen that ptlrpc_svcpt_stop_threads waits forever holding an
already-freed waitq.

This patch adds an error handling into ptlrpc_start_thread to fix
this problem.

Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-2889
Lustre-change: http://review.whamcloud.com/5552Signed-off-by: Hiroya Nozaki <nozaki.hiroya@jp.fujitsu.com>
Reviewed-by: Liang Zhen <liang.zhen@intel.com>
Reviewed-by: Nikitas Angelinas <nikitas_angelinas@xyratex.com>
Reviewed-by: Keith Mannthey <keith.mannthey@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Peng Tao <tao.peng@emc.com>
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/lustre/ptlrpc/service.c

@@ -2765,11 +2765,19 @@ int ptlrpc_start_thread(struct ptlrpc_service_part *svcpt, int wait)
 		CERROR("cannot start thread '%s': rc %d\n",
 		       thread->t_name, rc);
 		spin_lock(&svcpt->scp_lock);
-		list_del(&thread->t_link);
 		--svcpt->scp_nthrs_starting;
-		spin_unlock(&svcpt->scp_lock);
-
-		OBD_FREE(thread, sizeof(*thread));
+		if (thread_is_stopping(thread)) {
+			/* this ptlrpc_thread is being hanled
+			 * by ptlrpc_svcpt_stop_threads now
+			 */
+			thread_add_flags(thread, SVC_STOPPED);
+			wake_up(&thread->t_ctl_waitq);
+			spin_unlock(&svcpt->scp_lock);
+		} else {
+			list_del(&thread->t_link);
+			spin_unlock(&svcpt->scp_lock);
+			OBD_FREE_PTR(thread);
+		}
 		RETURN(rc);
 	}