avoid deadlock by calling begin_trans() before locking any inodes

1 files changed, 10 insertions, 4 deletions

diff --git a/sysfile.c b/sysfile.c
index ca54013..c9d3594 100644
--- a/sysfile.c
+++ b/sysfile.c
@@ -116,14 +116,16 @@ sys_link(void)
     return -1;
   if((ip = namei(old)) == 0)
     return -1;
+
+  begin_trans();
+
   ilock(ip);
   if(ip->type == T_DIR){
     iunlockput(ip);
+    commit_trans();
     return -1;
   }
 
-  begin_trans();
-
   ip->nlink++;
   iupdate(ip);
   iunlock(ip);
@@ -180,16 +182,21 @@ sys_unlink(void)
     return -1;
   if((dp = nameiparent(path, name)) == 0)
     return -1;
+
+  begin_trans();
+
   ilock(dp);
 
   // Cannot unlink "." or "..".
   if(namecmp(name, ".") == 0 || namecmp(name, "..") == 0){
     iunlockput(dp);
+    commit_trans();
     return -1;
   }
 
   if((ip = dirlookup(dp, name, &off)) == 0){
     iunlockput(dp);
+    commit_trans();
     return -1;
   }
   ilock(ip);
@@ -199,11 +206,10 @@ sys_unlink(void)
   if(ip->type == T_DIR && !isdirempty(ip)){
     iunlockput(ip);
     iunlockput(dp);
+    commit_trans();
     return -1;
   }
 
-  begin_trans();
-
   memset(&de, 0, sizeof(de));
   if(writei(dp, (char*)&de, off, sizeof(de)) != sizeof(de))
     panic("unlink: writei");