kernel-ark/fs/fat/fatent.c
OGAWA Hirofumi 98283bb49c fat: Fix the race of read/write the FAT12 entry
FAT12 entry is 12bits, so it needs 2 phase to update the value.  And
writer and reader access it without any lock, so reader can get the
half updated value.

This fixes the long standing race condition by adding a global
spinlock to only FAT12 for avoiding any impact against FAT16/32.

Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-07-16 10:31:01 -07:00

624 lines
15 KiB
C

/*
* Copyright (C) 2004, OGAWA Hirofumi
* Released under GPL v2.
*/
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/msdos_fs.h>
struct fatent_operations {
void (*ent_blocknr)(struct super_block *, int, int *, sector_t *);
void (*ent_set_ptr)(struct fat_entry *, int);
int (*ent_bread)(struct super_block *, struct fat_entry *,
int, sector_t);
int (*ent_get)(struct fat_entry *);
void (*ent_put)(struct fat_entry *, int);
int (*ent_next)(struct fat_entry *);
};
static DEFINE_SPINLOCK(fat12_entry_lock);
static void fat12_ent_blocknr(struct super_block *sb, int entry,
int *offset, sector_t *blocknr)
{
struct msdos_sb_info *sbi = MSDOS_SB(sb);
int bytes = entry + (entry >> 1);
WARN_ON(entry < FAT_START_ENT || sbi->max_cluster <= entry);
*offset = bytes & (sb->s_blocksize - 1);
*blocknr = sbi->fat_start + (bytes >> sb->s_blocksize_bits);
}
static void fat_ent_blocknr(struct super_block *sb, int entry,
int *offset, sector_t *blocknr)
{
struct msdos_sb_info *sbi = MSDOS_SB(sb);
int bytes = (entry << sbi->fatent_shift);
WARN_ON(entry < FAT_START_ENT || sbi->max_cluster <= entry);
*offset = bytes & (sb->s_blocksize - 1);
*blocknr = sbi->fat_start + (bytes >> sb->s_blocksize_bits);
}
static void fat12_ent_set_ptr(struct fat_entry *fatent, int offset)
{
struct buffer_head **bhs = fatent->bhs;
if (fatent->nr_bhs == 1) {
WARN_ON(offset >= (bhs[0]->b_size - 1));
fatent->u.ent12_p[0] = bhs[0]->b_data + offset;
fatent->u.ent12_p[1] = bhs[0]->b_data + (offset + 1);
} else {
WARN_ON(offset != (bhs[0]->b_size - 1));
fatent->u.ent12_p[0] = bhs[0]->b_data + offset;
fatent->u.ent12_p[1] = bhs[1]->b_data;
}
}
static void fat16_ent_set_ptr(struct fat_entry *fatent, int offset)
{
WARN_ON(offset & (2 - 1));
fatent->u.ent16_p = (__le16 *)(fatent->bhs[0]->b_data + offset);
}
static void fat32_ent_set_ptr(struct fat_entry *fatent, int offset)
{
WARN_ON(offset & (4 - 1));
fatent->u.ent32_p = (__le32 *)(fatent->bhs[0]->b_data + offset);
}
static int fat12_ent_bread(struct super_block *sb, struct fat_entry *fatent,
int offset, sector_t blocknr)
{
struct buffer_head **bhs = fatent->bhs;
WARN_ON(blocknr < MSDOS_SB(sb)->fat_start);
bhs[0] = sb_bread(sb, blocknr);
if (!bhs[0])
goto err;
if ((offset + 1) < sb->s_blocksize)
fatent->nr_bhs = 1;
else {
/* This entry is block boundary, it needs the next block */
blocknr++;
bhs[1] = sb_bread(sb, blocknr);
if (!bhs[1])
goto err_brelse;
fatent->nr_bhs = 2;
}
fat12_ent_set_ptr(fatent, offset);
return 0;
err_brelse:
brelse(bhs[0]);
err:
printk(KERN_ERR "FAT: FAT read failed (blocknr %llu)\n",
(unsigned long long)blocknr);
return -EIO;
}
static int fat_ent_bread(struct super_block *sb, struct fat_entry *fatent,
int offset, sector_t blocknr)
{
struct fatent_operations *ops = MSDOS_SB(sb)->fatent_ops;
WARN_ON(blocknr < MSDOS_SB(sb)->fat_start);
fatent->bhs[0] = sb_bread(sb, blocknr);
if (!fatent->bhs[0]) {
printk(KERN_ERR "FAT: FAT read failed (blocknr %llu)\n",
(unsigned long long)blocknr);
return -EIO;
}
fatent->nr_bhs = 1;
ops->ent_set_ptr(fatent, offset);
return 0;
}
static int fat12_ent_get(struct fat_entry *fatent)
{
u8 **ent12_p = fatent->u.ent12_p;
int next;
spin_lock(&fat12_entry_lock);
if (fatent->entry & 1)
next = (*ent12_p[0] >> 4) | (*ent12_p[1] << 4);
else
next = (*ent12_p[1] << 8) | *ent12_p[0];
spin_unlock(&fat12_entry_lock);
next &= 0x0fff;
if (next >= BAD_FAT12)
next = FAT_ENT_EOF;
return next;
}
static int fat16_ent_get(struct fat_entry *fatent)
{
int next = le16_to_cpu(*fatent->u.ent16_p);
WARN_ON((unsigned long)fatent->u.ent16_p & (2 - 1));
if (next >= BAD_FAT16)
next = FAT_ENT_EOF;
return next;
}
static int fat32_ent_get(struct fat_entry *fatent)
{
int next = le32_to_cpu(*fatent->u.ent32_p) & 0x0fffffff;
WARN_ON((unsigned long)fatent->u.ent32_p & (4 - 1));
if (next >= BAD_FAT32)
next = FAT_ENT_EOF;
return next;
}
static void fat12_ent_put(struct fat_entry *fatent, int new)
{
u8 **ent12_p = fatent->u.ent12_p;
if (new == FAT_ENT_EOF)
new = EOF_FAT12;
spin_lock(&fat12_entry_lock);
if (fatent->entry & 1) {
*ent12_p[0] = (new << 4) | (*ent12_p[0] & 0x0f);
*ent12_p[1] = new >> 4;
} else {
*ent12_p[0] = new & 0xff;
*ent12_p[1] = (*ent12_p[1] & 0xf0) | (new >> 8);
}
spin_unlock(&fat12_entry_lock);
mark_buffer_dirty(fatent->bhs[0]);
if (fatent->nr_bhs == 2)
mark_buffer_dirty(fatent->bhs[1]);
}
static void fat16_ent_put(struct fat_entry *fatent, int new)
{
if (new == FAT_ENT_EOF)
new = EOF_FAT16;
*fatent->u.ent16_p = cpu_to_le16(new);
mark_buffer_dirty(fatent->bhs[0]);
}
static void fat32_ent_put(struct fat_entry *fatent, int new)
{
if (new == FAT_ENT_EOF)
new = EOF_FAT32;
WARN_ON(new & 0xf0000000);
new |= le32_to_cpu(*fatent->u.ent32_p) & ~0x0fffffff;
*fatent->u.ent32_p = cpu_to_le32(new);
mark_buffer_dirty(fatent->bhs[0]);
}
static int fat12_ent_next(struct fat_entry *fatent)
{
u8 **ent12_p = fatent->u.ent12_p;
struct buffer_head **bhs = fatent->bhs;
u8 *nextp = ent12_p[1] + 1 + (fatent->entry & 1);
fatent->entry++;
if (fatent->nr_bhs == 1) {
WARN_ON(ent12_p[0] > (u8 *)(bhs[0]->b_data + (bhs[0]->b_size - 2)));
WARN_ON(ent12_p[1] > (u8 *)(bhs[0]->b_data + (bhs[0]->b_size - 1)));
if (nextp < (u8 *)(bhs[0]->b_data + (bhs[0]->b_size - 1))) {
ent12_p[0] = nextp - 1;
ent12_p[1] = nextp;
return 1;
}
} else {
WARN_ON(ent12_p[0] != (u8 *)(bhs[0]->b_data + (bhs[0]->b_size - 1)));
WARN_ON(ent12_p[1] != (u8 *)bhs[1]->b_data);
ent12_p[0] = nextp - 1;
ent12_p[1] = nextp;
brelse(bhs[0]);
bhs[0] = bhs[1];
fatent->nr_bhs = 1;
return 1;
}
ent12_p[0] = NULL;
ent12_p[1] = NULL;
return 0;
}
static int fat16_ent_next(struct fat_entry *fatent)
{
const struct buffer_head *bh = fatent->bhs[0];
fatent->entry++;
if (fatent->u.ent16_p < (__le16 *)(bh->b_data + (bh->b_size - 2))) {
fatent->u.ent16_p++;
return 1;
}
fatent->u.ent16_p = NULL;
return 0;
}
static int fat32_ent_next(struct fat_entry *fatent)
{
const struct buffer_head *bh = fatent->bhs[0];
fatent->entry++;
if (fatent->u.ent32_p < (__le32 *)(bh->b_data + (bh->b_size - 4))) {
fatent->u.ent32_p++;
return 1;
}
fatent->u.ent32_p = NULL;
return 0;
}
static struct fatent_operations fat12_ops = {
.ent_blocknr = fat12_ent_blocknr,
.ent_set_ptr = fat12_ent_set_ptr,
.ent_bread = fat12_ent_bread,
.ent_get = fat12_ent_get,
.ent_put = fat12_ent_put,
.ent_next = fat12_ent_next,
};
static struct fatent_operations fat16_ops = {
.ent_blocknr = fat_ent_blocknr,
.ent_set_ptr = fat16_ent_set_ptr,
.ent_bread = fat_ent_bread,
.ent_get = fat16_ent_get,
.ent_put = fat16_ent_put,
.ent_next = fat16_ent_next,
};
static struct fatent_operations fat32_ops = {
.ent_blocknr = fat_ent_blocknr,
.ent_set_ptr = fat32_ent_set_ptr,
.ent_bread = fat_ent_bread,
.ent_get = fat32_ent_get,
.ent_put = fat32_ent_put,
.ent_next = fat32_ent_next,
};
static inline void lock_fat(struct msdos_sb_info *sbi)
{
mutex_lock(&sbi->fat_lock);
}
static inline void unlock_fat(struct msdos_sb_info *sbi)
{
mutex_unlock(&sbi->fat_lock);
}
void fat_ent_access_init(struct super_block *sb)
{
struct msdos_sb_info *sbi = MSDOS_SB(sb);
mutex_init(&sbi->fat_lock);
switch (sbi->fat_bits) {
case 32:
sbi->fatent_shift = 2;
sbi->fatent_ops = &fat32_ops;
break;
case 16:
sbi->fatent_shift = 1;
sbi->fatent_ops = &fat16_ops;
break;
case 12:
sbi->fatent_shift = -1;
sbi->fatent_ops = &fat12_ops;
break;
}
}
static inline int fat_ent_update_ptr(struct super_block *sb,
struct fat_entry *fatent,
int offset, sector_t blocknr)
{
struct msdos_sb_info *sbi = MSDOS_SB(sb);
struct fatent_operations *ops = sbi->fatent_ops;
struct buffer_head **bhs = fatent->bhs;
/* Is this fatent's blocks including this entry? */
if (!fatent->nr_bhs || bhs[0]->b_blocknr != blocknr)
return 0;
/* Does this entry need the next block? */
if (sbi->fat_bits == 12 && (offset + 1) >= sb->s_blocksize) {
if (fatent->nr_bhs != 2 || bhs[1]->b_blocknr != (blocknr + 1))
return 0;
}
ops->ent_set_ptr(fatent, offset);
return 1;
}
int fat_ent_read(struct inode *inode, struct fat_entry *fatent, int entry)
{
struct super_block *sb = inode->i_sb;
struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
struct fatent_operations *ops = sbi->fatent_ops;
int err, offset;
sector_t blocknr;
if (entry < FAT_START_ENT || sbi->max_cluster <= entry) {
fatent_brelse(fatent);
fat_fs_panic(sb, "invalid access to FAT (entry 0x%08x)", entry);
return -EIO;
}
fatent_set_entry(fatent, entry);
ops->ent_blocknr(sb, entry, &offset, &blocknr);
if (!fat_ent_update_ptr(sb, fatent, offset, blocknr)) {
fatent_brelse(fatent);
err = ops->ent_bread(sb, fatent, offset, blocknr);
if (err)
return err;
}
return ops->ent_get(fatent);
}
/* FIXME: We can write the blocks as more big chunk. */
static int fat_mirror_bhs(struct super_block *sb, struct buffer_head **bhs,
int nr_bhs)
{
struct msdos_sb_info *sbi = MSDOS_SB(sb);
struct buffer_head *c_bh;
int err, n, copy;
err = 0;
for (copy = 1; copy < sbi->fats; copy++) {
sector_t backup_fat = sbi->fat_length * copy;
for (n = 0; n < nr_bhs; n++) {
c_bh = sb_getblk(sb, backup_fat + bhs[n]->b_blocknr);
if (!c_bh) {
err = -ENOMEM;
goto error;
}
memcpy(c_bh->b_data, bhs[n]->b_data, sb->s_blocksize);
set_buffer_uptodate(c_bh);
mark_buffer_dirty(c_bh);
if (sb->s_flags & MS_SYNCHRONOUS)
err = sync_dirty_buffer(c_bh);
brelse(c_bh);
if (err)
goto error;
}
}
error:
return err;
}
int fat_ent_write(struct inode *inode, struct fat_entry *fatent,
int new, int wait)
{
struct super_block *sb = inode->i_sb;
struct fatent_operations *ops = MSDOS_SB(sb)->fatent_ops;
int err;
ops->ent_put(fatent, new);
if (wait) {
err = fat_sync_bhs(fatent->bhs, fatent->nr_bhs);
if (err)
return err;
}
return fat_mirror_bhs(sb, fatent->bhs, fatent->nr_bhs);
}
static inline int fat_ent_next(struct msdos_sb_info *sbi,
struct fat_entry *fatent)
{
if (sbi->fatent_ops->ent_next(fatent)) {
if (fatent->entry < sbi->max_cluster)
return 1;
}
return 0;
}
static inline int fat_ent_read_block(struct super_block *sb,
struct fat_entry *fatent)
{
struct fatent_operations *ops = MSDOS_SB(sb)->fatent_ops;
sector_t blocknr;
int offset;
fatent_brelse(fatent);
ops->ent_blocknr(sb, fatent->entry, &offset, &blocknr);
return ops->ent_bread(sb, fatent, offset, blocknr);
}
static void fat_collect_bhs(struct buffer_head **bhs, int *nr_bhs,
struct fat_entry *fatent)
{
int n, i;
for (n = 0; n < fatent->nr_bhs; n++) {
for (i = 0; i < *nr_bhs; i++) {
if (fatent->bhs[n] == bhs[i])
break;
}
if (i == *nr_bhs) {
get_bh(fatent->bhs[n]);
bhs[i] = fatent->bhs[n];
(*nr_bhs)++;
}
}
}
int fat_alloc_clusters(struct inode *inode, int *cluster, int nr_cluster)
{
struct super_block *sb = inode->i_sb;
struct msdos_sb_info *sbi = MSDOS_SB(sb);
struct fatent_operations *ops = sbi->fatent_ops;
struct fat_entry fatent, prev_ent;
struct buffer_head *bhs[MAX_BUF_PER_PAGE];
int i, count, err, nr_bhs, idx_clus;
BUG_ON(nr_cluster > (MAX_BUF_PER_PAGE / 2)); /* fixed limit */
lock_fat(sbi);
if (sbi->free_clusters != -1 && sbi->free_clusters < nr_cluster) {
unlock_fat(sbi);
return -ENOSPC;
}
err = nr_bhs = idx_clus = 0;
count = FAT_START_ENT;
fatent_init(&prev_ent);
fatent_init(&fatent);
fatent_set_entry(&fatent, sbi->prev_free + 1);
while (count < sbi->max_cluster) {
if (fatent.entry >= sbi->max_cluster)
fatent.entry = FAT_START_ENT;
fatent_set_entry(&fatent, fatent.entry);
err = fat_ent_read_block(sb, &fatent);
if (err)
goto out;
/* Find the free entries in a block */
do {
if (ops->ent_get(&fatent) == FAT_ENT_FREE) {
int entry = fatent.entry;
/* make the cluster chain */
ops->ent_put(&fatent, FAT_ENT_EOF);
if (prev_ent.nr_bhs)
ops->ent_put(&prev_ent, entry);
fat_collect_bhs(bhs, &nr_bhs, &fatent);
sbi->prev_free = entry;
if (sbi->free_clusters != -1)
sbi->free_clusters--;
sb->s_dirt = 1;
cluster[idx_clus] = entry;
idx_clus++;
if (idx_clus == nr_cluster)
goto out;
/*
* fat_collect_bhs() gets ref-count of bhs,
* so we can still use the prev_ent.
*/
prev_ent = fatent;
}
count++;
if (count == sbi->max_cluster)
break;
} while (fat_ent_next(sbi, &fatent));
}
/* Couldn't allocate the free entries */
sbi->free_clusters = 0;
sb->s_dirt = 1;
err = -ENOSPC;
out:
unlock_fat(sbi);
fatent_brelse(&fatent);
if (!err) {
if (inode_needs_sync(inode))
err = fat_sync_bhs(bhs, nr_bhs);
if (!err)
err = fat_mirror_bhs(sb, bhs, nr_bhs);
}
for (i = 0; i < nr_bhs; i++)
brelse(bhs[i]);
if (err && idx_clus)
fat_free_clusters(inode, cluster[0]);
return err;
}
int fat_free_clusters(struct inode *inode, int cluster)
{
struct super_block *sb = inode->i_sb;
struct msdos_sb_info *sbi = MSDOS_SB(sb);
struct fatent_operations *ops = sbi->fatent_ops;
struct fat_entry fatent;
struct buffer_head *bhs[MAX_BUF_PER_PAGE];
int i, err, nr_bhs;
nr_bhs = 0;
fatent_init(&fatent);
lock_fat(sbi);
do {
cluster = fat_ent_read(inode, &fatent, cluster);
if (cluster < 0) {
err = cluster;
goto error;
} else if (cluster == FAT_ENT_FREE) {
fat_fs_panic(sb, "%s: deleting FAT entry beyond EOF",
__FUNCTION__);
err = -EIO;
goto error;
}
ops->ent_put(&fatent, FAT_ENT_FREE);
if (sbi->free_clusters != -1) {
sbi->free_clusters++;
sb->s_dirt = 1;
}
if (nr_bhs + fatent.nr_bhs > MAX_BUF_PER_PAGE) {
if (sb->s_flags & MS_SYNCHRONOUS) {
err = fat_sync_bhs(bhs, nr_bhs);
if (err)
goto error;
}
err = fat_mirror_bhs(sb, bhs, nr_bhs);
if (err)
goto error;
for (i = 0; i < nr_bhs; i++)
brelse(bhs[i]);
nr_bhs = 0;
}
fat_collect_bhs(bhs, &nr_bhs, &fatent);
} while (cluster != FAT_ENT_EOF);
if (sb->s_flags & MS_SYNCHRONOUS) {
err = fat_sync_bhs(bhs, nr_bhs);
if (err)
goto error;
}
err = fat_mirror_bhs(sb, bhs, nr_bhs);
error:
fatent_brelse(&fatent);
for (i = 0; i < nr_bhs; i++)
brelse(bhs[i]);
unlock_fat(sbi);
fat_clusters_flush(sb);
return err;
}
EXPORT_SYMBOL_GPL(fat_free_clusters);
int fat_count_free_clusters(struct super_block *sb)
{
struct msdos_sb_info *sbi = MSDOS_SB(sb);
struct fatent_operations *ops = sbi->fatent_ops;
struct fat_entry fatent;
int err = 0, free;
lock_fat(sbi);
if (sbi->free_clusters != -1)
goto out;
free = 0;
fatent_init(&fatent);
fatent_set_entry(&fatent, FAT_START_ENT);
while (fatent.entry < sbi->max_cluster) {
err = fat_ent_read_block(sb, &fatent);
if (err)
goto out;
do {
if (ops->ent_get(&fatent) == FAT_ENT_FREE)
free++;
} while (fat_ent_next(sbi, &fatent));
}
sbi->free_clusters = free;
sb->s_dirt = 1;
fatent_brelse(&fatent);
out:
unlock_fat(sbi);
return err;
}