MahnoKropotkinvich/xv6-labs-2024-solution
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debugging an unknown panic

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This commit is contained in:
whatever 2024-11-25 18:33:26 +08:00
parent c8587aba91
commit 39d5972dbd
5 changed files with 111 additions and 58 deletions
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BIN
fs.img.bk
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2
gradelib.py
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@ -238,7 +238,7 @@ def make(*target):
post_make()
def show_command(cmd):
from pipes import quote
from shlex import quote
print("\n$", " ".join(map(quote, cmd)))
def maybe_unlink(*paths):

160
kernel/bio.c
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@ -37,16 +37,16 @@ struct {
uint hash_head[NHASH];
uint nxt[NBUF];
struct spinlock hashlock[NHASH];
uint freelist_head;
uint freelist_head[NCPU];
// Linked list of all buffers, through prev/next.
// Sorted by how recently the buffer was used.
// head.next is most recent, head.prev is least.
// struct buf head;
struct spinlock freelistlock;
struct spinlock freelistlock[NCPU];
} bcache;
uint hasher(uint dev,uint blockno){
return blockno%NHASH;
return ((uint64)dev<<32|blockno)%NHASH;
}
int hash_get(uint dev,uint blockno){
@ -60,6 +60,7 @@ int hash_get(uint dev,uint blockno){
}
RET:
release(&bcache.hashlock[hash_pos]);
// printf("%u\n",pos);
return pos;
@ -75,16 +76,42 @@ void hash_add(uint dev,uint blockno,uint buf_pos){
void hash_del(uint dev,uint blockno){
const uint hash_pos=hasher(dev, blockno);
push_off();
const uint cpu=cpuid();
pop_off();
acquire(&bcache.hashlock[hash_pos]);
for(int cur=bcache.hash_head[hash_pos],pre=-2;cur!=-1;cur=bcache.nxt[cur]){
if(bcache.buf[cur].dev==dev && bcache.buf[cur].blockno==blockno){
if(pre==-2){// the head is what we are looking for
bcache.hash_head[hash_pos]=bcache.nxt[cur];
}else{
bcache.nxt[pre]=bcache.nxt[cur];
struct buf *b=&bcache.buf[cur];
--b->refcnt;
if (b->refcnt == 0) {
if(pre==-2){// the head is what we are looking for
bcache.hash_head[hash_pos]=bcache.nxt[cur];
}else{
bcache.nxt[pre]=bcache.nxt[cur];
}
bcache.nxt[cur]=-1;
for(int i=cpu;;i=(i+1)%NCPU){
push_off();
if(holding(&bcache.freelistlock[i])){
pop_off();
continue;
}
pop_off();
acquire(&bcache.freelistlock[i]);
const int pos=b-bcache.buf;
// printf("%d\n",pos);
bcache.nxt[pos]=bcache.freelist_head[i];
bcache.freelist_head[i]=pos;
// DEBUG();
// printf("%u\n",bcache.freelist_head);
release(&bcache.freelistlock[i]);
break;
}
break;
}
bcache.nxt[cur]=-1;
break;
}
pre=cur;
}
@ -97,22 +124,26 @@ binit(void)
struct buf *b;
initlock(&bcache.lock, "bcache");
initlock(&bcache.freelistlock, "bcache_freelist");
for(int i=0;i<NHASH;i++){
initlock(&bcache.hashlock[i], "bcache_hashtable");
bcache.hash_head[i]=-1;
}
bcache.freelist_head=-1;
for(int i=0;i<NCPU;++i){
bcache.freelist_head[i]=-1;
initlock(&bcache.freelistlock[i], "bcache_freelist");
}
// Create linked list of buffers
// bcache.head.prev = &bcache.head;
// bcache.head.next = &bcache.head;
int which=0;
for(b = bcache.buf; b < bcache.buf+NBUF; b++){
// b->next = bcache.head.next;
// b->prev = &bcache.head;
initsleeplock(&b->lock, "buffer");
const uint cur=b-bcache.buf;
bcache.nxt[cur]=bcache.freelist_head;
bcache.freelist_head=cur;
bcache.nxt[cur]=bcache.freelist_head[which];
bcache.freelist_head[which]=cur;
which=(which+1)%NCPU;
// bcache.head.next->prev = b;
// bcache.head.next = b;
}
@ -125,8 +156,8 @@ static struct buf*
bget(uint dev, uint blockno)
{
struct buf *b;
int pos=hash_get(dev, blockno);
// acquire(&bcache.lock);
const int pos=hash_get(dev, blockno);
// Is the block already cached?
// for(b = bcache.head.next; b != &bcache.head; b = b->next){
// if(b->dev == dev && b->blockno == blockno){
@ -138,39 +169,60 @@ bget(uint dev, uint blockno)
// }
if(pos>=0){
b=&bcache.buf[pos];
++b->refcnt;
const uint hash_pos=hasher(dev, blockno);
acquire(&bcache.hashlock[hash_pos]);
++bcache.buf[pos].refcnt;
release(&bcache.hashlock[hash_pos]);
acquiresleep(&b->lock);
// release(&bcache.lock);
return b;
}
push_off();
const uint cpu=cpuid();
pop_off();
// Not cached.
// Recycle the least recently used (LRU) unused buffer.
acquire(&bcache.freelistlock);
// for(b = bcache.head.prev; b != &bcache.head; b = b->prev){
// if(b->refcnt == 0) {
// hash_add(dev, blockno, b-bcache.buf);
// b->dev = dev;
// b->blockno = blockno;
// b->valid = 0;
// b->refcnt = 1;
// release(&bcache.lock);
// acquiresleep(&b->lock);
// return b;
// }
// }
// for(uint cur=bcache.freelist_head;cur!=-1;cur=bcache.nxt[cur])
// DEBUG();
// printf("%u\n",bcache.freelist_head);
b=&bcache.buf[bcache.freelist_head];
hash_add(dev,blockno,bcache.freelist_head);
b->dev=dev;
b->blockno=blockno;
b->valid=0;
b->refcnt=1;
bcache.freelist_head=bcache.nxt[bcache.freelist_head];
release(&bcache.freelistlock);
acquiresleep(&b->lock);
return b;
for(int i=cpu;;i=(i+1)%NCPU){
push_off();
if(holding(&bcache.freelistlock[i])){
pop_off();
continue;
}
pop_off();
acquire(&bcache.freelistlock[i]);
if(bcache.freelist_head[i]==-1){
release(&bcache.freelistlock[i]);
continue;
}
// DEBUG();
// for(b = bcache.head.prev; b != &bcache.head; b = b->prev){
// if(b->refcnt == 0) {
// hash_add(dev, blockno, b-bcache.buf);
// b->dev = dev;
// b->blockno = blockno;
// b->valid = 0;
// b->refcnt = 1;
// release(&bcache.lock);
// acquiresleep(&b->lock);
// return b;
// }
// }
// for(uint cur=bcache.freelist_head;cur!=-1;cur=bcache.nxt[cur])
// DEBUG();
// printf("%u\n",bcache.freelist_head);
b=&bcache.buf[bcache.freelist_head[i]];
const int ori=bcache.freelist_head[i];
bcache.freelist_head[i]=bcache.nxt[bcache.freelist_head[i]];
hash_add(dev,blockno,ori);
b->dev=dev;
b->blockno=blockno;
b->valid=0;
b->refcnt=1;
release(&bcache.freelistlock[i]);
acquiresleep(&b->lock);
// release(&bcache.lock);
return b;
}
panic("bget: no buffers");
}
@ -202,15 +254,15 @@ bwrite(struct buf *b)
void
brelse(struct buf *b)
{
if(!holdingsleep(&b->lock))
panic("brelse");
releasesleep(&b->lock);
// acquire(&bcache.lock);
b->refcnt--;
if (b->refcnt == 0) {
hash_del(b->dev, b->blockno);
hash_del(b->dev, b->blockno);
// no one is waiting for it.
// b->next->prev = b->prev;
// b->prev->next = b->next;
@ -218,16 +270,8 @@ brelse(struct buf *b)
// b->prev = &bcache.head;
// bcache.head.next->prev = b;
// bcache.head.next = b;gi
acquire(&bcache.freelistlock);
const int pos=b-bcache.buf;
bcache.nxt[pos]=bcache.freelist_head;
bcache.freelist_head=pos;
// DEBUG();
// printf("%u\n",bcache.freelist_head);
release(&bcache.freelistlock);
}
// release(&bcache.lock);
}
@ -235,14 +279,20 @@ brelse(struct buf *b)
void
bpin(struct buf *b) {
// acquire(&bcache.lock);
const uint hash_pos=hasher(b->dev, b->blockno);
acquire(&bcache.hashlock[hash_pos]);
b->refcnt++;
release(&bcache.hashlock[hash_pos]);
// release(&bcache.lock);
}
void
bunpin(struct buf *b) {
// acquire(&bcache.lock);
const uint hash_pos=hasher(b->dev, b->blockno);
acquire(&bcache.hashlock[hash_pos]);
b->refcnt--;
release(&bcache.hashlock[hash_pos]);
// release(&bcache.lock);
}

6
kernel/fs.c
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@ -93,12 +93,14 @@ bfree(int dev, uint b)
{
struct buf *bp;
int bi, m;
DEBUG();
printf("%d %d\n",dev,b);
bp = bread(dev, BBLOCK(b, sb));
bi = b % BPB;
m = 1 << (bi % 8);
if((bp->data[bi/8] & m) == 0)
if((bp->data[bi/8] & m) == 0){
panic("freeing free block");
}
bp->data[bi/8] &= ~m;
log_write(bp);
brelse(bp);

1
time.txt Normal file
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@ -0,0 +1 @@
6