From a4ee6f7de32bfbd73499ac7da19e69ad0741e993 Mon Sep 17 00:00:00 2001
From: Robert Morris <rtm@csail.mit.edu>
Date: Tue, 8 Aug 2017 14:19:54 -0400
Subject: [PATCH] fix iput() to more obviously avoid deadlock

---
 fs.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/fs.c b/fs.c
index 67616a46dd..8bec001966 100644
--- a/fs.c
+++ b/fs.c
@@ -329,20 +329,22 @@ iunlock(struct inode *ip)
 void
 iput(struct inode *ip)
 {
-  acquire(&icache.lock);
-  if(ip->ref == 1){
-    acquiresleep(&ip->lock);
-    if(ip->valid && ip->nlink == 0){
+  acquiresleep(&ip->lock);
+  if(ip->valid && ip->nlink == 0){
+    acquire(&icache.lock);
+    int r = ip->ref;
+    release(&icache.lock);
+    if(r == 1){
       // inode has no links and no other references: truncate and free.
-      release(&icache.lock);
       itrunc(ip);
       ip->type = 0;
       iupdate(ip);
       ip->valid = 0;
-      acquire(&icache.lock);
     }
-    releasesleep(&ip->lock);
   }
+  releasesleep(&ip->lock);
+
+  acquire(&icache.lock);
   ip->ref--;
   release(&icache.lock);
 }