From 0f399f5b78e19243f4f505884a35252bee93cee1 Mon Sep 17 00:00:00 2001
From: nfshp <nfshp>
Date: Sat, 14 Dec 2002 12:05:49 +0000
Subject: [PATCH] as Zach's pointed out, fix the potential deadlock, use
 wait_event() to sync between threads when liod start/stop.

---
 lustre/llite/iod.c | 50 +++++++++++++-------------------------------------
 1 file changed, 13 insertions(+), 37 deletions(-)

diff --git a/lustre/llite/iod.c b/lustre/llite/iod.c
index c748064..a2f58c6 100644
--- a/lustre/llite/iod.c
+++ b/lustre/llite/iod.c
@@ -34,18 +34,16 @@ static int liod_main(void *arg)
         sprintf(current->comm, "liod");
         unlock_kernel();
 
-        /* declear we are ready */
-	spin_lock(&iod->io_lock);
-	iod->io_flag |= LIOD_FLAG_ALIVE;
+        /* declare we are ready */
+	set_bit(LIOD_FLAG_ALIVE, &iod->io_flag);
         wake_up(&iod->io_waitq);
-	spin_unlock(&iod->io_lock);
 
         CDEBUG(D_NET, "liod(%d) started\n", current->pid);
         while (1) {
 		int t;
 
 		/* check the stop command */
-		if (iod->io_flag & LIOD_FLAG_STOP)
+		if (test_bit(LIOD_FLAG_STOP, &iod->io_flag))
 			break;
 
 		t = interruptible_sleep_on_timeout(&iod->io_sleepq,
@@ -54,11 +52,8 @@ static int liod_main(void *arg)
 				(t ? "wakeup" : "timeout"));
         }
 
-	spin_lock(&iod->io_lock);
-	iod->io_flag &= ~LIOD_FLAG_ALIVE;
-	iod->io_flag |= LIOD_FLAG_STOPPED;
+	clear_bit(LIOD_FLAG_ALIVE, &iod->io_flag);
         wake_up(&iod->io_waitq);
-	spin_unlock(&iod->io_lock);
 
         CDEBUG(D_NET, "liod(%d) exit\n", current->pid);
         RETURN(0);
@@ -66,40 +61,25 @@ static int liod_main(void *arg)
 
 int liod_start(struct ll_io_daemon *iod)
 {
-        DECLARE_WAITQUEUE(queue, current);
         int rc;
 
         /* initialize */
         iod->io_flag = 0;
-        spin_lock_init(&iod->io_lock);
         init_waitqueue_head(&iod->io_sleepq);
         init_waitqueue_head(&iod->io_waitq);
 
-        spin_lock(&iod->io_lock);
-
         rc = kernel_thread(liod_main, (void *) iod,
                            CLONE_VM | CLONE_FS | CLONE_FILES);
 
         if (rc < 0) {
 		CERROR("fail to start liod, error %d\n", rc);
-                spin_unlock(&iod->io_lock);
                 return rc;
         }
 
-        set_current_state(TASK_UNINTERRUPTIBLE);
-        add_wait_queue(&iod->io_waitq, &queue);
-        spin_unlock(&iod->io_lock);
-
 	/* wait liod start */
-        schedule();
-
-        set_current_state(TASK_RUNNING);
-        remove_wait_queue(&iod->io_waitq, &queue);
+	wait_event(iod->io_waitq, test_bit(LIOD_FLAG_ALIVE, &iod->io_flag));
 
-        if (iod->io_flag & LIOD_FLAG_ALIVE)
-                return 0;
-        else
-                return -ENOMEM;
+        return 0;
 }
 
 void liod_wakeup(struct ll_io_daemon *iod)
@@ -109,23 +89,19 @@ void liod_wakeup(struct ll_io_daemon *iod)
 
 void liod_stop(struct ll_io_daemon *iod)
 {
-        DECLARE_WAITQUEUE(queue, current);
-
-        spin_lock(&iod->io_lock);
+	if (!test_bit(LIOD_FLAG_ALIVE, &iod->io_flag)) {
+		CERROR("liod died unexpectedly!\n");
+		return;
+	}
 
         /* send the kill command */
-        iod->io_flag |= LIOD_FLAG_STOP;
+	set_bit(LIOD_FLAG_STOP, &iod->io_flag);
 
         /* if wakeup daemon */
         wake_up(&iod->io_sleepq);
 
-        /* wait daemon's exit */
-        set_current_state(TASK_UNINTERRUPTIBLE);
-        add_wait_queue(&iod->io_waitq, &queue);
-        spin_unlock(&iod->io_lock);
-
-        schedule();
-        /* must woken up by liod */
+	/* wait liod exit */
+	wait_event(iod->io_waitq, !test_bit(LIOD_FLAG_ALIVE, &iod->io_flag));
 
 	return;
 }
-- 
1.8.3.1