--- /dev/null
+kmem_cache_create: duplicate cache jbd_4k
+
+The jbd slab cache creation/deletion is racey. If multiple jbd based
+filesystems are mounted concurrently, and there are no other jbd based
+filesystems already mounted. Then we can race creating the slab caches
+since jbd_slab[] is not locked. This is not commonly observed because
+typically /root is mounted early with a jbd based filesystem making the
+race impossible. On our diskless systems /root does not use the jbd
+but we do have attached storage which does, and which is mounted in
+parallel. Basically our setup is similiar to what may be found in a
+NAS style appliance.
+
+This patch wraps all modifications to jbd_slab[] in the jbd_slab_lock
+to prevent this above race.
+
+LLNL Bug 291
+Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
+
+Index: linux+rh+chaos/fs/jbd/journal.c
+===================================================================
+--- linux+rh+chaos.orig/fs/jbd/journal.c
++++ linux+rh+chaos/fs/jbd/journal.c
+@@ -1979,6 +1979,7 @@ void * __jbd_kmalloc (const char *where,
+ #define JBD_MAX_SLABS 5
+ #define JBD_SLAB_INDEX(size) (size >> 11)
+
++static DECLARE_RWSEM(jbd_slab_lock); /* protect jbd_slab[] */
+ static kmem_cache_t *jbd_slab[JBD_MAX_SLABS];
+ static const char *jbd_slab_names[JBD_MAX_SLABS] = {
+ "jbd_1k", "jbd_2k", "jbd_4k", NULL, "jbd_8k"
+@@ -1988,24 +1989,27 @@ static void journal_destroy_jbd_slabs(vo
+ {
+ int i;
+
++ down_write(&jbd_slab_lock);
+ for (i = 0; i < JBD_MAX_SLABS; i++) {
+ if (jbd_slab[i])
+ kmem_cache_destroy(jbd_slab[i]);
+ jbd_slab[i] = NULL;
+ }
++ up_write(&jbd_slab_lock);
+ }
+
+ static int journal_create_jbd_slab(size_t slab_size)
+ {
+- int i = JBD_SLAB_INDEX(slab_size);
++ int rc = 0, i = JBD_SLAB_INDEX(slab_size);
+
+ BUG_ON(i >= JBD_MAX_SLABS);
+
+ /*
+ * Check if we already have a slab created for this size
+ */
++ down_write(&jbd_slab_lock);
+ if (jbd_slab[i])
+- return 0;
++ goto out_lock;
+
+ /*
+ * Create a slab and force alignment to be same as slabsize -
+@@ -2016,27 +2020,36 @@ static int journal_create_jbd_slab(size_
+ slab_size, slab_size, 0, NULL, NULL);
+ if (!jbd_slab[i]) {
+ printk(KERN_EMERG "JBD: no memory for jbd_slab cache\n");
+- return -ENOMEM;
++ rc = -ENOMEM;
+ }
+- return 0;
++out_lock:
++ up_write(&jbd_slab_lock);
++ return rc;
+ }
+
+ void * jbd_slab_alloc(size_t size, gfp_t flags)
+ {
++ void *ptr;
+ int idx;
+
++ down_read(&jbd_slab_lock);
+ idx = JBD_SLAB_INDEX(size);
+ BUG_ON(jbd_slab[idx] == NULL);
+- return kmem_cache_alloc(jbd_slab[idx], flags | __GFP_NOFAIL);
++ ptr = kmem_cache_alloc(jbd_slab[idx], flags | __GFP_NOFAIL);
++ up_read(&jbd_slab_lock);
++
++ return ptr;
+ }
+
+ void jbd_slab_free(void *ptr, size_t size)
+ {
+ int idx;
+
++ down_read(&jbd_slab_lock);
+ idx = JBD_SLAB_INDEX(size);
+ BUG_ON(jbd_slab[idx] == NULL);
+ kmem_cache_free(jbd_slab[idx], ptr);
++ up_read(&jbd_slab_lock);
+ }
+
+ /*
+
git://git.whamcloud.com / fs / lustre-release.git / commitdiff