Another version that drops the slub lock for both invocations of sysfs
functions from kmem_cache_create. The invocation from slab_sysfs_init
is not a problem since user space is not active at that point.
Subject: slub: Do not take the slub lock while calling into sysfs
This patch avoids holding the slub_lock during kmem_cache_create()
when calling sysfs. It is possible because kmem_cache_create()
allocates the kmem_cache object and therefore is the only one context
that can access the newly created object. It is therefore possible
to drop the slub_lock early. We defer the adding of the new kmem_cache
to the end of processing because the new kmem_cache structure would
be reachable otherwise via scans over slabs. This allows sysfs_slab_add()
to run without holding any locks.
The case is different if we are creating an alias instead of a new
kmem_cache structure. In that case we can also drop the slub lock
early because we have taken a refcount on the kmem_cache structure.
It therefore cannot vanish from under us.
But if the sysfs_slab_alias() call fails we can no longer simply
decrement the refcount since the other references may have gone
away in the meantime. Call kmem_cache_destroy() to cause the
refcount to be decremented and the kmem_cache structure to be
freed if all references are gone.
Signed-off-by: Christoph Lameter <cl@xxxxxxxxx>
---
mm/slub.c | 25 +++++++++++--------------
1 file changed, 11 insertions(+), 14 deletions(-)
Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c 2012-01-17 09:53:26.599505365 -0600
+++ linux-2.6/mm/slub.c 2012-01-17 09:59:57.131497273 -0600
@@ -3912,13 +3912,14 @@ struct kmem_cache *kmem_cache_create(con
s->objsize = max(s->objsize, (int)size);
s->inuse = max_t(int, s->inuse, ALIGN(size, sizeof(void *)));
+ up_write(&slub_lock);
if (sysfs_slab_alias(s, name)) {
- s->refcount--;
+ kmem_cache_destroy(s);
goto err;
}
- up_write(&slub_lock);
return s;
}
+ up_write(&slub_lock);
n = kstrdup(name, GFP_KERNEL);
if (!n)
@@ -3928,27 +3929,23 @@ struct kmem_cache *kmem_cache_create(con
if (s) {
if (kmem_cache_open(s, n,
size, align, flags, ctor)) {
- list_add(&s->list, &slab_caches);
- if (sysfs_slab_add(s)) {
- list_del(&s->list);
- kfree(n);
- kfree(s);
- goto err;
+
+ if (sysfs_slab_add(s) == 0) {
+ down_write(&slub_lock);
+ list_add(&s->list, &slab_caches);
+ up_write(&slub_lock);
+ return s;
}
- up_write(&slub_lock);
- return s;
}
kfree(n);
kfree(s);
}
err:
- up_write(&slub_lock);
if (flags & SLAB_PANIC)
panic("Cannot create slabcache %s\n", name);
- else
- s = NULL;
- return s;
+
+ return NULL;
}
EXPORT_SYMBOL(kmem_cache_create);
--
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