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 3a5fa7ed90.

Conflicts:

	defs.h
	file.c
	file.h
This commit is contained in:
Frans Kaashoek 2011-08-29 17:18:40 -04:00
parent 22f7db5336
commit 1ddfbbb194
12 changed files with 61 additions and 105 deletions

41
bio.c
View file

@ -13,7 +13,9 @@
// * Only one process at a time can use a buffer, // * Only one process at a time can use a buffer,
// so do not keep them longer than necessary. // 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 // * B_VALID: the buffer data has been initialized
// with the associated disk block contents. // with the associated disk block contents.
// * B_DIRTY: the buffer data has been modified // * B_DIRTY: the buffer data has been modified
@ -49,8 +51,6 @@ binit(void)
b->next = bcache.head.next; b->next = bcache.head.next;
b->prev = &bcache.head; b->prev = &bcache.head;
b->dev = -1; b->dev = -1;
initlock(&b->lock, "buf");
initsleeplock(&b->sleeplock);
bcache.head.next->prev = b; bcache.head.next->prev = b;
bcache.head.next = b; bcache.head.next = b;
} }
@ -58,43 +58,42 @@ binit(void)
// Look through buffer cache for sector on device dev. // Look through buffer cache for sector on device dev.
// If not found, allocate fresh block. // If not found, allocate fresh block.
// In either case, return sleep-locked buffer. // In either case, return locked buffer.
static struct buf* static struct buf*
bget(uint dev, uint sector) bget(uint dev, uint sector)
{ {
struct buf *b; struct buf *b;
acquire(&bcache.lock); acquire(&bcache.lock);
loop:
// Try for cached block. // Try for cached block.
for(b = bcache.head.next; b != &bcache.head; b = b->next){ for(b = bcache.head.next; b != &bcache.head; b = b->next){
acquire(&b->lock);
if(b->dev == dev && b->sector == sector){ if(b->dev == dev && b->sector == sector){
if(!(b->flags & B_BUSY)){
b->flags |= B_BUSY;
release(&bcache.lock); release(&bcache.lock);
acquire_sleeplock(&b->sleeplock, &b->lock);
release(&b->lock);
return b; return b;
} }
release(&b->lock); sleep(b, &bcache.lock);
goto loop;
}
} }
// Allocate fresh block. // Allocate fresh block.
for(b = bcache.head.prev; b != &bcache.head; b = b->prev){ for(b = bcache.head.prev; b != &bcache.head; b = b->prev){
acquire(&b->lock); if((b->flags & B_BUSY) == 0){
if (!acquired_sleeplock(&b->sleeplock)) {
release(&bcache.lock);
b->dev = dev; b->dev = dev;
b->sector = sector; b->sector = sector;
b->flags = 0; b->flags = B_BUSY;
acquire_sleeplock(&b->sleeplock, &b->lock); release(&bcache.lock);
release(&b->lock);
return b; return b;
} }
release(&b->lock);
} }
panic("bget: no buffers"); 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* struct buf*
bread(uint dev, uint sector) bread(uint dev, uint sector)
{ {
@ -110,7 +109,7 @@ bread(uint dev, uint sector)
void void
bwrite(struct buf *b) bwrite(struct buf *b)
{ {
if(!acquired_sleeplock(&b->sleeplock)) if((b->flags & B_BUSY) == 0)
panic("bwrite"); panic("bwrite");
b->flags |= B_DIRTY; b->flags |= B_DIRTY;
iderw(b); iderw(b);
@ -120,11 +119,11 @@ bwrite(struct buf *b)
void void
brelse(struct buf *b) brelse(struct buf *b)
{ {
if(!acquired_sleeplock(&b->sleeplock)) if((b->flags & B_BUSY) == 0)
panic("brelse"); panic("brelse");
acquire(&bcache.lock); acquire(&bcache.lock);
acquire(&b->lock);
b->next->prev = b->prev; b->next->prev = b->prev;
b->prev->next = b->next; b->prev->next = b->next;
b->next = bcache.head.next; b->next = bcache.head.next;
@ -132,8 +131,8 @@ brelse(struct buf *b)
bcache.head.next->prev = b; bcache.head.next->prev = b;
bcache.head.next = b; bcache.head.next = b;
release_sleeplock(&b->sleeplock); b->flags &= ~B_BUSY;
release(&b->lock); wakeup(b);
release(&bcache.lock); release(&bcache.lock);
} }

7
buf.h
View file

@ -2,13 +2,12 @@ struct buf {
int flags; int flags;
uint dev; uint dev;
uint sector; uint sector;
struct spinlock lock;
struct sleeplock sleeplock;
struct buf *prev; // LRU cache list struct buf *prev; // LRU cache list
struct buf *next; struct buf *next;
struct buf *qnext; // disk queue struct buf *qnext; // disk queue
uchar data[512]; uchar data[512];
}; };
#define B_VALID 0x1 // buffer has been read from disk #define B_BUSY 0x1 // buffer is locked by some process
#define B_DIRTY 0x2 // buffer needs to be written to disk #define B_VALID 0x2 // buffer has been read from disk
#define B_DIRTY 0x4 // buffer needs to be written to disk

5
defs.h
View file

@ -5,7 +5,6 @@ struct inode;
struct pipe; struct pipe;
struct proc; struct proc;
struct spinlock; struct spinlock;
struct sleeplock;
struct stat; struct stat;
struct superblock; struct superblock;
@ -130,10 +129,6 @@ void initlock(struct spinlock*, char*);
void release(struct spinlock*); void release(struct spinlock*);
void pushcli(void); void pushcli(void);
void popcli(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 // string.c
int memcmp(const void*, const void*, uint); int memcmp(const void*, const void*, uint);

2
file.c
View file

@ -2,8 +2,8 @@
#include "defs.h" #include "defs.h"
#include "param.h" #include "param.h"
#include "fs.h" #include "fs.h"
#include "spinlock.h"
#include "file.h" #include "file.h"
#include "spinlock.h"
struct devsw devsw[NDEV]; struct devsw devsw[NDEV];
struct { struct {

7
file.h
View file

@ -15,9 +15,7 @@ struct inode {
uint dev; // Device number uint dev; // Device number
uint inum; // Inode number uint inum; // Inode number
int ref; // Reference count int ref; // Reference count
int flags; // I_VALID int flags; // I_BUSY, I_VALID
struct spinlock lock;
struct sleeplock sleeplock;
short type; // copy of disk inode short type; // copy of disk inode
short major; short major;
@ -27,7 +25,8 @@ struct inode {
uint addrs[NDIRECT+1]; uint addrs[NDIRECT+1];
}; };
#define I_VALID 0x1 #define I_BUSY 0x1
#define I_VALID 0x2
// device implementations // device implementations

32
fs.c
View file

@ -113,8 +113,11 @@ bfree(int dev, uint b)
// It is an error to use an inode without holding a reference to it. // It is an error to use an inode without holding a reference to it.
// //
// Processes are only allowed to read and write inode // Processes are only allowed to read and write inode
// metadata and contents when holding the inode's sleeplock. // metadata and contents when holding the inode's lock,
// Callers are responsible for locking // 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 // inodes before passing them to routines in this file; leaving
// this responsibility with the caller makes it possible for them // this responsibility with the caller makes it possible for them
// to create arbitrarily-sized atomic operations. // to create arbitrarily-sized atomic operations.
@ -213,7 +216,6 @@ iget(uint dev, uint inum)
ip->inum = inum; ip->inum = inum;
ip->ref = 1; ip->ref = 1;
ip->flags = 0; ip->flags = 0;
initsleeplock(&ip->sleeplock);
release(&icache.lock); release(&icache.lock);
return ip; return ip;
@ -230,7 +232,7 @@ idup(struct inode *ip)
return ip; return ip;
} }
// Acquire the sleeplock for a given inode. // Lock the given inode.
void void
ilock(struct inode *ip) ilock(struct inode *ip)
{ {
@ -241,7 +243,9 @@ ilock(struct inode *ip)
panic("ilock"); panic("ilock");
acquire(&icache.lock); 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); release(&icache.lock);
if(!(ip->flags & I_VALID)){ if(!(ip->flags & I_VALID)){
@ -264,11 +268,12 @@ ilock(struct inode *ip)
void void
iunlock(struct inode *ip) 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"); panic("iunlock");
acquire(&icache.lock); acquire(&icache.lock);
release_sleeplock(&ip->sleeplock); ip->flags &= ~I_BUSY;
wakeup(ip);
release(&icache.lock); release(&icache.lock);
} }
@ -279,15 +284,14 @@ iput(struct inode *ip)
acquire(&icache.lock); acquire(&icache.lock);
if(ip->ref == 1 && (ip->flags & I_VALID) && ip->nlink == 0){ if(ip->ref == 1 && (ip->flags & I_VALID) && ip->nlink == 0){
// inode is no longer used: truncate and free inode. // inode is no longer used: truncate and free inode.
if(acquired_sleeplock(&ip->sleeplock)) if(ip->flags & I_BUSY)
panic("iput busy"); panic("iput busy");
acquire_sleeplock(&ip->sleeplock, &icache.lock); ip->flags |= I_BUSY;
release(&icache.lock); release(&icache.lock);
itrunc(ip); itrunc(ip);
ip->type = 0; ip->type = 0;
iupdate(ip); iupdate(ip);
acquire(&icache.lock); acquire(&icache.lock);
release_sleeplock(&ip->sleeplock);
ip->flags = 0; ip->flags = 0;
wakeup(ip); wakeup(ip);
} }
@ -429,14 +433,10 @@ writei(struct inode *ip, char *src, uint off, uint n)
return devsw[ip->major].write(ip, src, n); return devsw[ip->major].write(ip, src, n);
} }
if(off > ip->size || off + n < off) { if(off > ip->size || off + n < off)
panic("writei1");
return -1; return -1;
} if(off + n > MAXFILE*BSIZE)
if(off + n > MAXFILE*BSIZE) {
panic("writei2");
return -1; return -1;
}
for(tot=0; tot<n; tot+=m, off+=m, src+=m){ for(tot=0; tot<n; tot+=m, off+=m, src+=m){
bp = bread(ip->dev, bmap(ip, off/BSIZE)); bp = bread(ip->dev, bmap(ip, off/BSIZE));

2
ide.c
View file

@ -127,7 +127,7 @@ iderw(struct buf *b)
{ {
struct buf **pp; struct buf **pp;
if(!acquired_sleeplock(&b->sleeplock)) if(!(b->flags & B_BUSY))
panic("iderw: buf not busy"); panic("iderw: buf not busy");
if((b->flags & (B_VALID|B_DIRTY)) == B_VALID) if((b->flags & (B_VALID|B_DIRTY)) == B_VALID)
panic("iderw: nothing to do"); panic("iderw: nothing to do");

14
log.c
View file

@ -43,9 +43,9 @@ struct logheader {
struct { struct {
struct spinlock lock; struct spinlock lock;
struct sleeplock sleeplock;
int start; int start;
int size; int size;
int intrans;
int dev; int dev;
struct logheader lh; struct logheader lh;
} log; } log;
@ -60,7 +60,6 @@ initlog(void)
struct superblock sb; struct superblock sb;
initlock(&log.lock, "log"); initlock(&log.lock, "log");
initsleeplock(&log.sleeplock);
readsb(ROOTDEV, &sb); readsb(ROOTDEV, &sb);
log.start = sb.size - sb.nlog; log.start = sb.size - sb.nlog;
log.size = sb.nlog; log.size = sb.nlog;
@ -134,7 +133,10 @@ void
begin_trans(void) begin_trans(void)
{ {
acquire(&log.lock); acquire(&log.lock);
acquire_sleeplock(&log.sleeplock, &log.lock); while (log.intrans) {
sleep(&log, &log.lock);
}
log.intrans = 1;
release(&log.lock); release(&log.lock);
} }
@ -147,8 +149,10 @@ commit_trans(void)
log.lh.n = 0; log.lh.n = 0;
write_head(); // Reclaim log write_head(); // Reclaim log
} }
acquire(&log.lock); acquire(&log.lock);
release_sleeplock(&log.sleeplock); log.intrans = 0;
wakeup(&log);
release(&log.lock); release(&log.lock);
} }
@ -167,7 +171,7 @@ log_write(struct buf *b)
if (log.lh.n >= LOGSIZE || log.lh.n >= log.size - 1) if (log.lh.n >= LOGSIZE || log.lh.n >= log.size - 1)
panic("too big a transaction"); panic("too big a transaction");
if (!acquired_sleeplock(&log.sleeplock)) if (!log.intrans)
panic("write outside of trans"); panic("write outside of trans");
// cprintf("log_write: %d %d\n", b->sector, log.lh.n); // cprintf("log_write: %d %d\n", b->sector, log.lh.n);

2
pipe.c
View file

@ -4,8 +4,8 @@
#include "mmu.h" #include "mmu.h"
#include "proc.h" #include "proc.h"
#include "fs.h" #include "fs.h"
#include "spinlock.h"
#include "file.h" #include "file.h"
#include "spinlock.h"
#define PIPESIZE 512 #define PIPESIZE 512

View file

@ -17,9 +17,10 @@ initlock(struct spinlock *lk, char *name)
lk->cpu = 0; lk->cpu = 0;
} }
// Acquire a spin lock. Loops (spins) until the lock is acquired. // Acquire the lock.
// Holding a lock for a long time may cause other CPUs to waste time spinning to acquire it. // Loops (spins) until the lock is acquired.
// Spinlocks shouldn't be held across sleep(); for those cases, use sleeplocks. // Holding a lock for a long time may cause
// other CPUs to waste time spinning to acquire it.
void void
acquire(struct spinlock *lk) acquire(struct spinlock *lk)
{ {
@ -114,38 +115,3 @@ popcli(void)
sti(); 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;
}

View file

@ -1,4 +1,4 @@
// Mutual exclusion lock for short code fragments // Mutual exclusion lock.
struct spinlock { struct spinlock {
uint locked; // Is the lock held? uint locked; // Is the lock held?
@ -9,8 +9,3 @@ struct spinlock {
// that locked the lock. // that locked the lock.
}; };
// Lock that maybe held across sleeps
struct sleeplock {
uint locked; // Is the lock held?
};

View file

@ -5,7 +5,6 @@
#include "mmu.h" #include "mmu.h"
#include "proc.h" #include "proc.h"
#include "fs.h" #include "fs.h"
#include "spinlock.h"
#include "file.h" #include "file.h"
#include "fcntl.h" #include "fcntl.h"