[PATCH] slab: don't BUG on duplicated cache

slab presently goes BUG if someone tries to register an already-registered
cache.

But this can happen if the user accidentally loads a module which is already
statically linked into the kernel.  Nuking the kernel is rather a harsh
reaction.

Change it into a warning, and just fail the kmem_cache_alloc() attempt.  If
the module is well-behaved, the modprobe will fail and all is well.

Notes:

- Swaps the ranking of cache_chain_sem and lock_cpu_hotplug().  Doesn't seem
  important.

Acked-by: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/mm/slab.c b/mm/slab.c
index 22bfb0b..41e9179 100644 (file)
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1502,6 +1502,7 @@ kmem_cache_create (const char *name, size_t size, size_t align,
 {
        size_t left_over, slab_size, ralign;
        kmem_cache_t *cachep = NULL;
+       struct list_head *p;
 
        /*
         * Sanity checks... these are all serious usage bugs.
@@ -1516,6 +1517,35 @@ kmem_cache_create (const char *name, size_t size, size_t align,
                        BUG();
                }
 
+       down(&cache_chain_sem);
+
+       list_for_each(p, &cache_chain) {
+               kmem_cache_t *pc = list_entry(p, kmem_cache_t, next);
+               mm_segment_t old_fs = get_fs();
+               char tmp;
+               int res;
+
+               /*
+                * This happens when the module gets unloaded and doesn't
+                * destroy its slab cache and no-one else reuses the vmalloc
+                * area of the module.  Print a warning.
+                */
+               set_fs(KERNEL_DS);
+               res = __get_user(tmp, pc->name);
+               set_fs(old_fs);
+               if (res) {
+                       printk("SLAB: cache with size %d has lost its name\n",
+                                       pc->objsize);
+                       continue;
+               }
+
+               if (!strcmp(pc->name,name)) {
+                       printk("kmem_cache_create: duplicate cache %s\n", name);
+                       dump_stack();
+                       goto oops;
+               }
+       }
+
 #if DEBUG
        WARN_ON(strchr(name, ' '));     /* It confuses parsers */
        if ((flags & SLAB_DEBUG_INITIAL) && !ctor) {
@@ -1592,7 +1622,7 @@ kmem_cache_create (const char *name, size_t size, size_t align,
        /* Get cache's description obj. */
        cachep = (kmem_cache_t *) kmem_cache_alloc(&cache_cache, SLAB_KERNEL);
        if (!cachep)
-               goto opps;
+               goto oops;
        memset(cachep, 0, sizeof(kmem_cache_t));
 
 #if DEBUG
@@ -1686,7 +1716,7 @@ next:
                printk("kmem_cache_create: couldn't create cache %s.\n", name);
                kmem_cache_free(&cache_cache, cachep);
                cachep = NULL;
-               goto opps;
+               goto oops;
        }
        slab_size = ALIGN(cachep->num*sizeof(kmem_bufctl_t)
                                + sizeof(struct slab), align);
@@ -1781,43 +1811,14 @@ next:
                cachep->limit = BOOT_CPUCACHE_ENTRIES;
        } 
 
-       /* Need the semaphore to access the chain. */
-       down(&cache_chain_sem);
-       {
-               struct list_head *p;
-               mm_segment_t old_fs;
-
-               old_fs = get_fs();
-               set_fs(KERNEL_DS);
-               list_for_each(p, &cache_chain) {
-                       kmem_cache_t *pc = list_entry(p, kmem_cache_t, next);
-                       char tmp;
-                       /* This happens when the module gets unloaded and doesn't
-                          destroy its slab cache and noone else reuses the vmalloc
-                          area of the module. Print a warning. */
-                       if (__get_user(tmp,pc->name)) { 
-                               printk("SLAB: cache with size %d has lost its name\n", 
-                                       pc->objsize); 
-                               continue; 
-                       }       
-                       if (!strcmp(pc->name,name)) { 
-                               printk("kmem_cache_create: duplicate cache %s\n",name); 
-                               up(&cache_chain_sem); 
-                               unlock_cpu_hotplug();
-                               BUG(); 
-                       }       
-               }
-               set_fs(old_fs);
-       }
-
        /* cache setup completed, link it into the list */
        list_add(&cachep->next, &cache_chain);
-       up(&cache_chain_sem);
        unlock_cpu_hotplug();
-opps:
+oops:
        if (!cachep && (flags & SLAB_PANIC))
                panic("kmem_cache_create(): failed to create slab `%s'\n",
                        name);
+       up(&cache_chain_sem);
        return cachep;
 }
 EXPORT_SYMBOL(kmem_cache_create);