From 5053dd6a6d2b481bfcddbd91bacc885b9f0e0ff5 Mon Sep 17 00:00:00 2001
From: Robert Morris <rtm@csail.mit.edu>
Date: Mon, 15 Aug 2011 12:44:20 -0400
Subject: [PATCH] avoid deadlock by calling begin_trans() before locking any
inodes
---
file.c | 6 ++++--
fs.c | 7 +++----
log.c | 4 ++--
sysfile.c | 14 ++++++++++----
usertests.c | 50 +++++++++++++++++++++++++++++++++++++++++++++++---
5 files changed, 66 insertions(+), 15 deletions(-)
diff --git a/file.c b/file.c
index 7101a50..f8a14ad 100644
--- a/file.c
+++ b/file.c
@@ -118,7 +118,6 @@ filewrite(struct file *f, char *addr, int n)
if(f->type == FD_PIPE)
return pipewrite(f->pipe, addr, n);
if(f->type == FD_INODE){
- ilock(f->ip);
// write a few blocks at a time to avoid exceeding
// the maximum log transaction size, including
// i-node, indirect block, allocation blocks,
@@ -131,9 +130,13 @@ filewrite(struct file *f, char *addr, int n)
int n1 = n - i;
if(n1 > max)
n1 = max;
+
begin_trans();
+ ilock(f->ip);
r = writei(f->ip, addr + i, f->off, n1);
+ iunlock(f->ip);
commit_trans();
+
if(r < 0)
break;
if(r != n1)
@@ -141,7 +144,6 @@ filewrite(struct file *f, char *addr, int n)
f->off += r;
i += r;
}
- iunlock(f->ip);
return i == n ? n : -1;
}
panic("filewrite");
diff --git a/fs.c b/fs.c
index a76788b..fe9ce48 100644
--- a/fs.c
+++ b/fs.c
@@ -43,13 +43,13 @@ bzero(int dev, int bno)
bp = bread(dev, bno);
memset(bp->data, 0, BSIZE);
- bwrite(bp);
+ log_write(bp);
brelse(bp);
}
// Blocks.
-// Allocate a disk block.
+// Allocate a zeroed disk block.
static uint
balloc(uint dev)
{
@@ -67,6 +67,7 @@ balloc(uint dev)
bp->data[bi/8] |= m; // Mark block in use on disk.
log_write(bp);
brelse(bp);
+ bzero(dev, b + bi);
return b + bi;
}
}
@@ -83,8 +84,6 @@ bfree(int dev, uint b)
struct superblock sb;
int bi, m;
- bzero(dev, b);
-
readsb(dev, &sb);
bp = bread(dev, BBLOCK(b, sb.ninodes));
bi = b % BPB;
diff --git a/log.c b/log.c
index db36ba9..e9a16c5 100644
--- a/log.c
+++ b/log.c
@@ -124,9 +124,9 @@ static void
recover_from_log(void)
{
read_head();
- install_trans(); // Install all transactions till head
+ install_trans(); // if committed, copy from log to disk
log.lh.n = 0;
- write_head(); // Reclaim log
+ write_head(); // clear the log
}
void
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");
diff --git a/usertests.c b/usertests.c
index ba648a7..8db8385 100644
--- a/usertests.c
+++ b/usertests.c
@@ -364,6 +364,8 @@ sharedfd(void)
int fd, pid, i, n, nc, np;
char buf[10];
+ printf(1, "sharedfd test\n");
+
unlink("sharedfd");
fd = open("sharedfd", O_CREATE|O_RDWR);
if(fd < 0){
@@ -655,7 +657,7 @@ linktest(void)
printf(1, "linktest ok\n");
}
-// test concurrent create and unlink of the same file
+// test concurrent create/link/unlink of the same file
void
concreate(void)
{
@@ -728,10 +730,15 @@ concreate(void)
}
if(((i % 3) == 0 && pid == 0) ||
((i % 3) == 1 && pid != 0)){
- fd = open(file, 0);
- close(fd);
+ close(open(file, 0));
+ close(open(file, 0));
+ close(open(file, 0));
+ close(open(file, 0));
} else {
unlink(file);
+ unlink(file);
+ unlink(file);
+ unlink(file);
}
if(pid == 0)
exit();
@@ -742,6 +749,42 @@ concreate(void)
printf(1, "concreate ok\n");
}
+// another concurrent link/unlink/create test,
+// to look for deadlocks.
+void
+linkunlink()
+{
+ int pid, i;
+
+ printf(1, "linkunlink test\n");
+
+ unlink("x");
+ pid = fork();
+ if(pid < 0){
+ printf(1, "fork failed\n");
+ exit();
+ }
+
+ unsigned int x = (pid ? 1 : 97);
+ for(i = 0; i < 100; i++){
+ x = x * 1103515245 + 12345;
+ if((x % 3) == 0){
+ close(open("x", O_RDWR | O_CREATE));
+ } else if((x % 3) == 1){
+ link("cat", "x");
+ } else {
+ unlink("x");
+ }
+ }
+
+ if(pid)
+ wait();
+ else
+ exit();
+
+ printf(1, "linkunlink ok\n");
+}
+
// directory that uses indirect blocks
void
bigdir(void)
@@ -1518,6 +1561,7 @@ main(int argc, char *argv[])
bigfile();
subdir();
concreate();
+ linkunlink();
linktest();
unlinkread();
createdelete();
--
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