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Subject[PATCH] fat_cache is not SMP safe (2.4.0-prerelease)
When copying large files to/from my vfat filesystem, I frequently get NULL
pointer dereference oopsen. I believe this to be a possible solution.
(I have been unable to cause an oops since I did this.)

(against 2.4.0-prerelease)

--- fs/fat/cache.c.orig Mon Jan 1 14:33:43 2001
+++ fs/fat/cache.c Mon Jan 1 19:13:29 2001
@@ -24,6 +24,7 @@
#endif

static struct fat_cache *fat_cache,cache[FAT_CACHE];
+spinlock_t fat_cache_lock = SPIN_LOCK_UNLOCKED;

/* Returns the this'th FAT entry, -1 if it is an end-of-file entry. If
new_value is != -1, that FAT entry is replaced by it. */
@@ -133,13 +134,16 @@
return next;
}

-
void fat_cache_init(void)
{
static int initialized = 0;
int count;

- if (initialized) return;
+ spin_lock(&fat_cache_lock);
+ if (initialized) {
+ spin_unlock(&fat_cache_lock);
+ return;
+ }
fat_cache = &cache[0];
for (count = 0; count < FAT_CACHE; count++) {
cache[count].device = 0;
@@ -147,6 +151,7 @@
&cache[count+1];
}
initialized = 1;
+ spin_unlock(&fat_cache_lock);
}


@@ -157,6 +162,7 @@

if (!first)
return;
+ spin_lock(&fat_cache_lock);
for (walk = fat_cache; walk; walk = walk->next)
if (inode->i_dev == walk->device
&& walk->start_cluster == first
@@ -166,8 +172,12 @@
#ifdef DEBUG
printk("cache hit: %d (%d)\n",walk->file_cluster,*d_clu);
#endif
- if ((*f_clu = walk->file_cluster) == cluster) return;
+ if ((*f_clu = walk->file_cluster) == cluster) {
+ spin_unlock(&fat_cache_lock);
+ return;
+ }
}
+ spin_unlock(&fat_cache_lock);
#ifdef DEBUG
printk("cache miss\n");
#endif
@@ -197,6 +207,7 @@
int first = MSDOS_I(inode)->i_start;

last = NULL;
+ spin_lock(&fat_cache_lock);
for (walk = fat_cache; walk->next; walk = (last = walk)->next)
if (inode->i_dev == walk->device
&& walk->start_cluster == first
@@ -204,17 +215,22 @@
if (walk->disk_cluster != d_clu) {
printk("FAT cache corruption inode=%ld\n",
inode->i_ino);
+ spin_unlock(&fat_cache_lock);
fat_cache_inval_inode(inode);
return;
}
/* update LRU */
- if (last == NULL) return;
+ if (last == NULL) {
+ spin_unlock(&fat_cache_lock);
+ return;
+ }
last->next = walk->next;
walk->next = fat_cache;
fat_cache = walk;
#ifdef DEBUG
list_cache();
#endif
+ spin_unlock(&fat_cache_lock);
return;
}
walk->device = inode->i_dev;
@@ -224,6 +240,7 @@
last->next = NULL;
walk->next = fat_cache;
fat_cache = walk;
+ spin_unlock(&fat_cache_lock);
#ifdef DEBUG
list_cache();
#endif
@@ -238,10 +255,12 @@
struct fat_cache *walk;
int first = MSDOS_I(inode)->i_start;

+ spin_lock(&fat_cache_lock);
for (walk = fat_cache; walk; walk = walk->next)
if (walk->device == inode->i_dev
&& walk->start_cluster == first)
walk->device = 0;
+ spin_unlock(&fat_cache_lock);
}


@@ -249,9 +268,11 @@
{
struct fat_cache *walk;

+ spin_lock(&fat_cache_lock);
for (walk = fat_cache; walk; walk = walk->next)
if (walk->device == device)
walk->device = 0;
+ spin_unlock(&fat_cache_lock);
}


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