Re: [PATCH] Fix 2.5.3pre reiserfs BUG() at boot time

Andi Kleen
2002-01-25T22:16:17Z

On Fri, Jan 25, 2002 at 01:38:14PM -0700, Andreas Dilger wrote:
> So, what exactly does the above do now (hint: p and pc are both local
> so they cannot be referenced anywhere else)? It used to check that you
> weren't trying to add two caches with the same name. This isn't
> possible with caches from broken modules anymore as they have no name.

I have fixed the loop now to check for names again.

> When calling kmem_cache_destroy() on a non-empty slab we should just
> malloc some memory with the old cache name + "_leaked" for the name
> pointer. At least then we have a sane chance of figuring out what caused
> the problem, instead of having a bunch of "broken" entries in the table,
> and remove the above "broken" check entirely (we will always have a name).

I don't like this because it complicates the code too much.
"broken" should be enough to debug it.

New patch appended. Linus please apply if you didn't already.

-Andi

Index: mm/slab.c
===================================================================
RCS file: /cvs/linux/mm/slab.c,v
retrieving revision 1.66
diff -u -u -r1.66 slab.c
--- mm/slab.c 2002/01/08 16:00:20 1.66
+++ mm/slab.c 2002/01/25 22:14:40
@@ -186,8 +186,6 @@
* manages a cache.
*/

-#define CACHE_NAMELEN 20 /* max name length for a slab cache */
-
struct kmem_cache_s {
/* 1) each alloc & free */
/* full, partial first, then free */
@@ -225,7 +223,7 @@
unsigned long failures;

/* 3) cache creation/removal */
- char name[CACHE_NAMELEN];
+ const char *name;
struct list_head next;
#ifdef CONFIG_SMP
/* 4) per-cpu data */
@@ -335,6 +333,7 @@
kmem_cache_t *cs_dmacachep;
} cache_sizes_t;

+/* These are the default caches for kmalloc. Custom caches can have other sizes. */
static cache_sizes_t cache_sizes[] = {
#if PAGE_SIZE == 4096
{ 32, NULL, NULL},
@@ -353,6 +352,26 @@
{131072, NULL, NULL},
{ 0, NULL, NULL}
};
+/* Must match cache_sizes above. Out of line to keep cache footprint low. */
+#define CN(x) { x, x ## "(DMA)" }
+static char cache_names[][2][18] = {
+#if PAGE_SIZE == 4096
+ CN("size-32"),
+#endif
+ CN("size-64"),
+ CN("size-128"),
+ CN("size-256"),
+ CN("size-512"),
+ CN("size-1024"),
+ CN("size-2048"),
+ CN("size-4096"),
+ CN("size-8192"),
+ CN("size-16384"),
+ CN("size-32768"),
+ CN("size-65536"),
+ CN("size-131072")
+};
+#undef CN

/* internal cache of cache description objs */
static kmem_cache_t cache_cache = {
@@ -437,7 +456,6 @@
void __init kmem_cache_sizes_init(void)
{
cache_sizes_t *sizes = cache_sizes;
- char name[20];
/*
* Fragmentation resistance on low memory - only use bigger
* page orders on machines with more than 32MB of memory.
@@ -450,9 +468,9 @@
* eliminates "false sharing".
* Note for systems short on memory removing the alignment will
* allow tighter packing of the smaller caches. */
- sprintf(name,"size-%Zd",sizes->cs_size);
if (!(sizes->cs_cachep =
- kmem_cache_create(name, sizes->cs_size,
+ kmem_cache_create(cache_names[sizes-cache_sizes][0],
+ sizes->cs_size,
0, SLAB_HWCACHE_ALIGN, NULL, NULL))) {
BUG();
}
@@ -462,9 +480,10 @@
offslab_limit = sizes->cs_size-sizeof(slab_t);
offslab_limit /= 2;
}
- sprintf(name, "size-%Zd(DMA)",sizes->cs_size);
- sizes->cs_dmacachep = kmem_cache_create(name, sizes->cs_size, 0,
- SLAB_CACHE_DMA|SLAB_HWCACHE_ALIGN, NULL, NULL);
+ sizes->cs_dmacachep = kmem_cache_create(
+ cache_names[sizes-cache_sizes][1],
+ sizes->cs_size, 0,
+ SLAB_CACHE_DMA|SLAB_HWCACHE_ALIGN, NULL, NULL);
if (!sizes->cs_dmacachep)
BUG();
sizes++;
@@ -604,6 +623,11 @@
* Cannot be called within a int, but can be interrupted.
* The @ctor is run when new pages are allocated by the cache
* and the @dtor is run before the pages are handed back.
+ *
+ * @name must be valid until the cache is destroyed. This implies that
+ * the module calling this has to destroy the cache before getting
+ * unloaded.
+ *
* The flags are
*
* %SLAB_POISON - Poison the slab with a known test pattern (a5a5a5a5)
@@ -632,7 +656,6 @@
* Sanity checks... these are all serious usage bugs.
*/
if ((!name) ||
- ((strlen(name) >= CACHE_NAMELEN - 1)) ||
in_interrupt() ||
(size < BYTES_PER_WORD) ||
(size > (1<<MAX_OBJ_ORDER)*PAGE_SIZE) ||
@@ -797,8 +820,7 @@
cachep->slabp_cache = kmem_find_general_cachep(slab_size,0);
cachep->ctor = ctor;
cachep->dtor = dtor;
- /* Copy name over so we don't have problems with unloaded modules */
- strcpy(cachep->name, name);
+ cachep->name = name;

#ifdef CONFIG_SMP
if (g_cpucache_up)
@@ -811,10 +833,11 @@

list_for_each(p, &cache_chain) {
kmem_cache_t *pc = list_entry(p, kmem_cache_t, next);
-
- /* The name field is constant - no lock needed. */
- if (!strcmp(pc->name, name))
- BUG();
+ char tmp;
+ if (get_user(tmp,pc->name))
+ continue;
+ if (!strcmp(pc->name,name))
+ BUG();
}
}

@@ -1878,6 +1901,7 @@
unsigned long num_objs;
unsigned long active_slabs = 0;
unsigned long num_slabs;
+ const char *name;
cachep = list_entry(p, kmem_cache_t, next);

spin_lock_irq(&cachep->spinlock);
@@ -1906,8 +1930,15 @@
num_slabs+=active_slabs;
num_objs = num_slabs*cachep->num;

+ name = cachep->name;
+ {
+ char tmp;
+ if (get_user(tmp, name))
+ name = "broken";
+ }
+
len += sprintf(page+len, "%-17s %6lu %6lu %6u %4lu %4lu %4u",
- cachep->name, active_objs, num_objs, cachep->objsize,
+ name, active_objs, num_objs, cachep->objsize,
active_slabs, num_slabs, (1<<cachep->gfporder));

#if STATS