ext4: make grpinfo slab cache names static

In 2.6.37 I was running into oopses with repeated module
loads & unloads.  I tracked this down to:

fb1813f4 ext4: use dedicated slab caches for group_info structures

(this was in addition to the features advert unload problem)

The kstrdup & subsequent kfree of the cache name was causing
a double free.  In slub, at least, if I read it right it allocates
& frees the name itself, slab seems to do something different...
so in slub I think we were leaking -our- cachep->name, and double
freeing the one allocated by slub.

After getting lost in slab/slub/slob a bit, I just looked at other
sized-caches that get allocated.  jbd2, biovec, sgpool all do it
more or less the way jbd2 does.  Below patch follows the jbd2
method of dynamically allocating a cache at mount time from
a list of static names.

(This might also possibly fix a race creating the caches with
parallel mounts running).

[Folded in a fix from Dan Carpenter which fixed an off-by-one error in
the original patch]

Cc: stable@kernel.org
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 60 insertions, 40 deletions

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 851f49b2f9d2..d1fe09aea73d 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -342,10 +342,15 @@ static struct kmem_cache *ext4_free_ext_cachep;
 /* We create slab caches for groupinfo data structures based on the
  * superblock block size.  There will be one per mounted filesystem for
  * each unique s_blocksize_bits */
-#define NR_GRPINFO_CACHES       \
-        (EXT4_MAX_BLOCK_LOG_SIZE - EXT4_MIN_BLOCK_LOG_SIZE + 1)
+#define NR_GRPINFO_CACHES 8
 static struct kmem_cache *ext4_groupinfo_caches[NR_GRPINFO_CACHES];
 
+static const char *ext4_groupinfo_slab_names[NR_GRPINFO_CACHES] = {
+        "ext4_groupinfo_1k", "ext4_groupinfo_2k", "ext4_groupinfo_4k",
+        "ext4_groupinfo_8k", "ext4_groupinfo_16k", "ext4_groupinfo_32k",
+        "ext4_groupinfo_64k", "ext4_groupinfo_128k"
+};
+
 static void ext4_mb_generate_from_pa(struct super_block *sb, void *bitmap,
                                         ext4_group_t group);
 static void ext4_mb_generate_from_freelist(struct super_block *sb, void *bitmap,
@@ -2414,6 +2419,55 @@ err_freesgi:
         return -ENOMEM;
 }
 
+static void ext4_groupinfo_destroy_slabs(void)
+{
+        int i;
+
+        for (i = 0; i < NR_GRPINFO_CACHES; i++) {
+                if (ext4_groupinfo_caches[i])
+                        kmem_cache_destroy(ext4_groupinfo_caches[i]);
+                ext4_groupinfo_caches[i] = NULL;
+        }
+}
+
+static int ext4_groupinfo_create_slab(size_t size)
+{
+        static DEFINE_MUTEX(ext4_grpinfo_slab_create_mutex);
+        int slab_size;
+        int blocksize_bits = order_base_2(size);
+        int cache_index = blocksize_bits - EXT4_MIN_BLOCK_LOG_SIZE;
+        struct kmem_cache *cachep;
+
+        if (cache_index >= NR_GRPINFO_CACHES)
+                return -EINVAL;
+
+        if (unlikely(cache_index < 0))
+                cache_index = 0;
+
+        mutex_lock(&ext4_grpinfo_slab_create_mutex);
+        if (ext4_groupinfo_caches[cache_index]) {
+                mutex_unlock(&ext4_grpinfo_slab_create_mutex);
+                return 0;       /* Already created */
+        }
+
+        slab_size = offsetof(struct ext4_group_info,
+                                bb_counters[blocksize_bits + 2]);
+
+        cachep = kmem_cache_create(ext4_groupinfo_slab_names[cache_index],
+                                        slab_size, 0, SLAB_RECLAIM_ACCOUNT,
+                                        NULL);
+
+        mutex_unlock(&ext4_grpinfo_slab_create_mutex);
+        if (!cachep) {
+                printk(KERN_EMERG "EXT4: no memory for groupinfo slab cache\n");
+                return -ENOMEM;
+        }
+
+        ext4_groupinfo_caches[cache_index] = cachep;
+
+        return 0;
+}
+
 int ext4_mb_init(struct super_block *sb, int needs_recovery)
 {
         struct ext4_sb_info *sbi = EXT4_SB(sb);
@@ -2421,9 +2475,6 @@ int ext4_mb_init(struct super_block *sb, int needs_recovery)
         unsigned offset;
         unsigned max;
         int ret;
-        int cache_index;
-        struct kmem_cache *cachep;
-        char *namep = NULL;
 
         i = (sb->s_blocksize_bits + 2) * sizeof(*sbi->s_mb_offsets);
 
@@ -2440,30 +2491,9 @@ int ext4_mb_init(struct super_block *sb, int needs_recovery)
                 goto out;
         }
 
-        cache_index = sb->s_blocksize_bits - EXT4_MIN_BLOCK_LOG_SIZE;
-        cachep = ext4_groupinfo_caches[cache_index];
-        if (!cachep) {
-                char name[32];
-                int len = offsetof(struct ext4_group_info,
-                                        bb_counters[sb->s_blocksize_bits + 2]);
-
-                sprintf(name, "ext4_groupinfo_%d", sb->s_blocksize_bits);
-                namep = kstrdup(name, GFP_KERNEL);
-                if (!namep) {
-                        ret = -ENOMEM;
-                        goto out;
-                }
-
-                /* Need to free the kmem_cache_name() when we
-                 * destroy the slab */
-                cachep = kmem_cache_create(namep, len, 0,
-                                             SLAB_RECLAIM_ACCOUNT, NULL);
-                if (!cachep) {
-                        ret = -ENOMEM;
-                        goto out;
-                }
-                ext4_groupinfo_caches[cache_index] = cachep;
-        }
+        ret = ext4_groupinfo_create_slab(sb->s_blocksize);
+        if (ret < 0)
+                goto out;
 
         /* order 0 is regular bitmap */
         sbi->s_mb_maxs[0] = sb->s_blocksize << 3;
@@ -2520,7 +2550,6 @@ out:
         if (ret) {
                 kfree(sbi->s_mb_offsets);
                 kfree(sbi->s_mb_maxs);
-                kfree(namep);
         }
         return ret;
 }
@@ -2734,7 +2763,6 @@ int __init ext4_init_mballoc(void)
 
 void ext4_exit_mballoc(void)
 {
-        int i;
         /*
          * Wait for completion of call_rcu()'s on ext4_pspace_cachep
          * before destroying the slab cache.
@@ -2743,15 +2771,7 @@ void ext4_exit_mballoc(void)
         kmem_cache_destroy(ext4_pspace_cachep);
         kmem_cache_destroy(ext4_ac_cachep);
         kmem_cache_destroy(ext4_free_ext_cachep);
-
-        for (i = 0; i < NR_GRPINFO_CACHES; i++) {
-                struct kmem_cache *cachep = ext4_groupinfo_caches[i];
-                if (cachep) {
-                        char *name = (char *)kmem_cache_name(cachep);
-                        kmem_cache_destroy(cachep);
-                        kfree(name);
-                }
-        }
+        ext4_groupinfo_destroy_slabs();
         ext4_remove_debugfs_entry();
 }