Revert "Introduce and use sleeplocks instead of BUSY flags"

My changes have a race with re-used bufs and the code doesn't seem to get shorter
Keep the changes that fixed ip->off race

This reverts commit 3a5fa7ed9020eaf8ab843a16d26db7393b2ec072.

Conflicts:

	defs.h
	file.c
	file.h

12 files changed, 61 insertions, 105 deletions

diff --git a/bio.c b/bio.c
index f11328d..6a3968b 100644
--- a/bio.c
+++ b/bio.c
@@ -13,7 +13,9 @@
 // * Only one process at a time can use a buffer,
 //     so do not keep them longer than necessary.
 // 
-// The implementation uses two state flags internally:
+// The implementation uses three state flags internally:
+// * B_BUSY: the block has been returned from bread
+//     and has not been passed back to brelse.  
 // * B_VALID: the buffer data has been initialized
 //     with the associated disk block contents.
 // * B_DIRTY: the buffer data has been modified
@@ -49,8 +51,6 @@ binit(void)
     b->next = bcache.head.next;
     b->prev = &bcache.head;
     b->dev = -1;
-    initlock(&b->lock, "buf");
-    initsleeplock(&b->sleeplock);
     bcache.head.next->prev = b;
     bcache.head.next = b;
   }
@@ -58,43 +58,42 @@ binit(void)
 
 // Look through buffer cache for sector on device dev.
 // If not found, allocate fresh block.
-// In either case, return sleep-locked buffer.
+// In either case, return locked buffer.
 static struct buf*
 bget(uint dev, uint sector)
 {
   struct buf *b;
 
   acquire(&bcache.lock);
+
+ loop:
   // Try for cached block.
   for(b = bcache.head.next; b != &bcache.head; b = b->next){
-    acquire(&b->lock);
     if(b->dev == dev && b->sector == sector){
-      release(&bcache.lock);
-      acquire_sleeplock(&b->sleeplock, &b->lock);
-      release(&b->lock);
-      return b;
+      if(!(b->flags & B_BUSY)){
+        b->flags |= B_BUSY;
+        release(&bcache.lock);
+        return b;
+      }
+      sleep(b, &bcache.lock);
+      goto loop;
     }
-    release(&b->lock);
   }
 
   // Allocate fresh block.
   for(b = bcache.head.prev; b != &bcache.head; b = b->prev){
-    acquire(&b->lock);
-    if (!acquired_sleeplock(&b->sleeplock)) {
-      release(&bcache.lock);
+    if((b->flags & B_BUSY) == 0){
       b->dev = dev;
       b->sector = sector;
-      b->flags = 0;
-      acquire_sleeplock(&b->sleeplock, &b->lock);
-      release(&b->lock);
+      b->flags = B_BUSY;
+      release(&bcache.lock);
       return b;
     }
-    release(&b->lock);
   }
   panic("bget: no buffers");
 }
 
-// Return a locked buf with the contents of the indicated disk sector.
+// Return a B_BUSY buf with the contents of the indicated disk sector.
 struct buf*
 bread(uint dev, uint sector)
 {
@@ -110,7 +109,7 @@ bread(uint dev, uint sector)
 void
 bwrite(struct buf *b)
 {
-  if(!acquired_sleeplock(&b->sleeplock))
+  if((b->flags & B_BUSY) == 0)
     panic("bwrite");
   b->flags |= B_DIRTY;
   iderw(b);
@@ -120,11 +119,11 @@ bwrite(struct buf *b)
 void
 brelse(struct buf *b)
 {
-  if(!acquired_sleeplock(&b->sleeplock))
+  if((b->flags & B_BUSY) == 0)
     panic("brelse");
 
   acquire(&bcache.lock);
-  acquire(&b->lock);
+
   b->next->prev = b->prev;
   b->prev->next = b->next;
   b->next = bcache.head.next;
@@ -132,8 +131,8 @@ brelse(struct buf *b)
   bcache.head.next->prev = b;
   bcache.head.next = b;
 
-  release_sleeplock(&b->sleeplock);
-  release(&b->lock);
+  b->flags &= ~B_BUSY;
+  wakeup(b);
 
   release(&bcache.lock);
 }
diff --git a/buf.h b/buf.h
index cfeb8c6..9c586f2 100644
--- a/buf.h
+++ b/buf.h
@@ -2,13 +2,12 @@ struct buf {
   int flags;
   uint dev;
   uint sector;
-  struct spinlock lock;
-  struct sleeplock sleeplock;
   struct buf *prev; // LRU cache list
   struct buf *next;
   struct buf *qnext; // disk queue
   uchar data[512];
 };
-#define B_VALID 0x1  // buffer has been read from disk
-#define B_DIRTY 0x2  // buffer needs to be written to disk
+#define B_BUSY  0x1  // buffer is locked by some process
+#define B_VALID 0x2  // buffer has been read from disk
+#define B_DIRTY 0x4  // buffer needs to be written to disk
 
diff --git a/defs.h b/defs.h
index 0a55759..19d559b 100644
--- a/defs.h
+++ b/defs.h
@@ -5,7 +5,6 @@ struct inode;
 struct pipe;
 struct proc;
 struct spinlock;
-struct sleeplock;
 struct stat;
 struct superblock;
 
@@ -130,10 +129,6 @@ void            initlock(struct spinlock*, char*);
 void            release(struct spinlock*);
 void            pushcli(void);
 void            popcli(void);
-void            initsleeplock(struct sleeplock*);
-void            acquire_sleeplock(struct sleeplock*, struct spinlock*);
-void            release_sleeplock(struct sleeplock*);
-int             acquired_sleeplock(struct sleeplock*);
 
 // string.c
 int             memcmp(const void*, const void*, uint);
diff --git a/file.c b/file.c
index df90e07..f28365e 100644
--- a/file.c
+++ b/file.c
@@ -2,8 +2,8 @@
 #include "defs.h"
 #include "param.h"
 #include "fs.h"
-#include "spinlock.h"
 #include "file.h"
+#include "spinlock.h"
 
 struct devsw devsw[NDEV];
 struct {
diff --git a/file.h b/file.h
index 2b4a2cb..d123696 100644
--- a/file.h
+++ b/file.h
@@ -15,9 +15,7 @@ struct inode {
   uint dev;           // Device number
   uint inum;          // Inode number
   int ref;            // Reference count
-  int flags;          // I_VALID
-  struct spinlock lock;
-  struct sleeplock sleeplock;
+  int flags;          // I_BUSY, I_VALID
 
   short type;         // copy of disk inode
   short major;
@@ -27,7 +25,8 @@ struct inode {
   uint addrs[NDIRECT+1];
 };
 
-#define I_VALID 0x1
+#define I_BUSY 0x1
+#define I_VALID 0x2
 
 // device implementations
 
diff --git a/fs.c b/fs.c
index 6bfe963..b755c78 100644
--- a/fs.c
+++ b/fs.c
@@ -113,8 +113,11 @@ bfree(int dev, uint b)
 // It is an error to use an inode without holding a reference to it.
 //
 // Processes are only allowed to read and write inode
-// metadata and contents when holding the inode's sleeplock.
-// Callers are responsible for locking
+// metadata and contents when holding the inode's lock,
+// represented by the I_BUSY flag in the in-memory copy.
+// Because inode locks are held during disk accesses, 
+// they are implemented using a flag rather than with
+// spin locks.  Callers are responsible for locking
 // inodes before passing them to routines in this file; leaving
 // this responsibility with the caller makes it possible for them
 // to create arbitrarily-sized atomic operations.
@@ -213,7 +216,6 @@ iget(uint dev, uint inum)
   ip->inum = inum;
   ip->ref = 1;
   ip->flags = 0;
-  initsleeplock(&ip->sleeplock);
   release(&icache.lock);
 
   return ip;
@@ -230,7 +232,7 @@ idup(struct inode *ip)
   return ip;
 }
 
-// Acquire the sleeplock for a given inode.
+// Lock the given inode.
 void
 ilock(struct inode *ip)
 {
@@ -241,7 +243,9 @@ ilock(struct inode *ip)
     panic("ilock");
 
   acquire(&icache.lock);
-  acquire_sleeplock(&ip->sleeplock, &icache.lock);
+  while(ip->flags & I_BUSY)
+    sleep(ip, &icache.lock);
+  ip->flags |= I_BUSY;
   release(&icache.lock);
 
   if(!(ip->flags & I_VALID)){
@@ -264,11 +268,12 @@ ilock(struct inode *ip)
 void
 iunlock(struct inode *ip)
 {
-  if(ip == 0 || !acquired_sleeplock(&ip->sleeplock) || ip->ref < 1)
+  if(ip == 0 || !(ip->flags & I_BUSY) || ip->ref < 1)
     panic("iunlock");
 
   acquire(&icache.lock);
-  release_sleeplock(&ip->sleeplock);
+  ip->flags &= ~I_BUSY;
+  wakeup(ip);
   release(&icache.lock);
 }
 
@@ -279,15 +284,14 @@ iput(struct inode *ip)
   acquire(&icache.lock);
   if(ip->ref == 1 && (ip->flags & I_VALID) && ip->nlink == 0){
     // inode is no longer used: truncate and free inode.
-    if(acquired_sleeplock(&ip->sleeplock))
+    if(ip->flags & I_BUSY)
       panic("iput busy");
-    acquire_sleeplock(&ip->sleeplock, &icache.lock);
+    ip->flags |= I_BUSY;
     release(&icache.lock);
     itrunc(ip);
     ip->type = 0;
     iupdate(ip);
     acquire(&icache.lock);
-    release_sleeplock(&ip->sleeplock);
     ip->flags = 0;
     wakeup(ip);
   }
@@ -429,14 +433,10 @@ writei(struct inode *ip, char *src, uint off, uint n)
     return devsw[ip->major].write(ip, src, n);
   }
 
-  if(off > ip->size || off + n < off) {
-    panic("writei1");
+  if(off > ip->size || off + n < off)
     return -1;
-  }
-  if(off + n > MAXFILE*BSIZE) {
-    panic("writei2");
+  if(off + n > MAXFILE*BSIZE)
     return -1;
-  }
 
   for(tot=0; tot<n; tot+=m, off+=m, src+=m){
     bp = bread(ip->dev, bmap(ip, off/BSIZE));
diff --git a/ide.c b/ide.c
index e41437e..4165831 100644
--- a/ide.c
+++ b/ide.c
@@ -127,7 +127,7 @@ iderw(struct buf *b)
 {
   struct buf **pp;
 
-  if(!acquired_sleeplock(&b->sleeplock))
+  if(!(b->flags & B_BUSY))
     panic("iderw: buf not busy");
   if((b->flags & (B_VALID|B_DIRTY)) == B_VALID)
     panic("iderw: nothing to do");
diff --git a/log.c b/log.c
index d2dcba7..6b5c329 100644
--- a/log.c
+++ b/log.c
@@ -43,9 +43,9 @@ struct logheader {
 
 struct {
   struct spinlock lock;
-  struct sleeplock sleeplock;
   int start;
   int size;
+  int intrans;
   int dev;
   struct logheader lh;
 } log;
@@ -60,7 +60,6 @@ initlog(void)
 
   struct superblock sb;
   initlock(&log.lock, "log");
-  initsleeplock(&log.sleeplock);
   readsb(ROOTDEV, &sb);
   log.start = sb.size - sb.nlog;
   log.size = sb.nlog;
@@ -134,7 +133,10 @@ void
 begin_trans(void)
 {
   acquire(&log.lock);
-  acquire_sleeplock(&log.sleeplock, &log.lock);
+  while (log.intrans) {
+    sleep(&log, &log.lock);
+  }
+  log.intrans = 1;
   release(&log.lock);
 }
 
@@ -147,8 +149,10 @@ commit_trans(void)
     log.lh.n = 0; 
     write_head();        // Reclaim log
   }
+  
   acquire(&log.lock);
-  release_sleeplock(&log.sleeplock);
+  log.intrans = 0;
+  wakeup(&log);
   release(&log.lock);
 }
 
@@ -167,7 +171,7 @@ log_write(struct buf *b)
 
   if (log.lh.n >= LOGSIZE || log.lh.n >= log.size - 1)
     panic("too big a transaction");
-  if (!acquired_sleeplock(&log.sleeplock))
+  if (!log.intrans)
     panic("write outside of trans");
 
   // cprintf("log_write: %d %d\n", b->sector, log.lh.n);
diff --git a/pipe.c b/pipe.c
index bbac4dc..f76ed5c 100644
--- a/pipe.c
+++ b/pipe.c
@@ -4,8 +4,8 @@
 #include "mmu.h"
 #include "proc.h"
 #include "fs.h"
-#include "spinlock.h"
 #include "file.h"
+#include "spinlock.h"
 
 #define PIPESIZE 512
 
diff --git a/spinlock.c b/spinlock.c
index c1f6a96..a16621c 100644
--- a/spinlock.c
+++ b/spinlock.c
@@ -17,9 +17,10 @@ initlock(struct spinlock *lk, char *name)
   lk->cpu = 0;
 }
 
-// Acquire a spin lock. Loops (spins) until the lock is acquired.
-// Holding a lock for a long time may cause other CPUs to waste time spinning to acquire it.
-// Spinlocks shouldn't be held across sleep(); for those cases, use sleeplocks.
+// Acquire the lock.
+// Loops (spins) until the lock is acquired.
+// Holding a lock for a long time may cause
+// other CPUs to waste time spinning to acquire it.
 void
 acquire(struct spinlock *lk)
 {
@@ -114,38 +115,3 @@ popcli(void)
     sti();
 }
 
-void
-initsleeplock(struct sleeplock *l)
-{
-  l->locked = 0;
-}
-
-// Grab the sleeplock that is protected by spinl. Sleeplocks allow a process to lock
-// a data structure for long times, including across sleeps.  Other processes that try
-// to acquire a sleeplock will be put to sleep when another process hold the sleeplock.
-// To update status of the sleeplock atomically, the caller must hold spinl
-void
-acquire_sleeplock(struct sleeplock *sleepl, struct spinlock *spinl)
-{
-  while (sleepl->locked) {
-    sleep(sleepl, spinl);
-  }
-  sleepl->locked = 1;
-}
-
-// Release the sleeplock that is protected by a spin lock
-// Caller must hold the spinlock that protects the sleeplock
-void
-release_sleeplock(struct sleeplock *sleepl)
-{
-  sleepl->locked = 0;
-  wakeup(sleepl);
-}
-
-// Is the sleeplock acquired?
-// Caller must hold the spinlock that protects the sleeplock
-int
-acquired_sleeplock(struct sleeplock *sleepl)
-{
-  return sleepl->locked;
-}
diff --git a/spinlock.h b/spinlock.h
index f6a69b7..fdda016 100644
--- a/spinlock.h
+++ b/spinlock.h
@@ -1,4 +1,4 @@
-// Mutual exclusion lock for short code fragments
+// Mutual exclusion lock.
 struct spinlock {
   uint locked;       // Is the lock held?
   
@@ -9,8 +9,3 @@ struct spinlock {
                      // that locked the lock.
 };
 
-// Lock that maybe held across sleeps
-struct sleeplock {
-  uint locked;       // Is the lock held?
-};
-
diff --git a/sysfile.c b/sysfile.c
index 11895df..c9d3594 100644
--- a/sysfile.c
+++ b/sysfile.c
@@ -5,7 +5,6 @@
 #include "mmu.h"
 #include "proc.h"
 #include "fs.h"
-#include "spinlock.h"
 #include "file.h"
 #include "fcntl.h"