From 70d912b332328cb30cd86fdf63074cf10ba5ed35 Mon Sep 17 00:00:00 2001
From: Robert Morris <rtm@csail.mit.edu>
Date: Tue, 8 Aug 2017 13:48:48 -0400
Subject: [PATCH] protect ip->valid and ip->nlink with sleep lock in iput()

---
 file.h |  4 ++--
 fs.c   | 18 ++++++++++--------
 2 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/file.h b/file.h
index 73a8e67..497a58a 100644
--- a/file.h
+++ b/file.h
@@ -14,8 +14,8 @@ struct inode {
   uint dev;           // Device number
   uint inum;          // Inode number
   int ref;            // Reference count
-  struct sleeplock lock;
-  int valid;          // remainder has been read from disk?
+  struct sleeplock lock; // protects everything below here
+  int valid;          // inode has been read from disk?
 
   short type;         // copy of disk inode
   short major;
diff --git a/fs.c b/fs.c
index b67db5d..c73c530 100644
--- a/fs.c
+++ b/fs.c
@@ -320,15 +320,17 @@ void
 iput(struct inode *ip)
 {
   acquire(&icache.lock);
-  if(ip->ref == 1 && ip->valid && ip->nlink == 0){
-    // inode has no links and no other references: truncate and free.
+  if(ip->ref == 1){
     acquiresleep(&ip->lock);
-    release(&icache.lock);
-    itrunc(ip);
-    ip->type = 0;
-    iupdate(ip);
-    acquire(&icache.lock);
-    ip->valid = 0;
+    if(ip->valid && ip->nlink == 0){
+      // 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);
   }
   ip->ref--;