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mm, slab: unlink slabinfo, sysfs and debugfs immediately

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kmem_cache_destroy() includes removing the associated sysfs and debugfs
directories, and the cache from the list of caches that appears in
/proc/slabinfo. Currently this might not happen immediately when:

- the cache is SLAB_TYPESAFE_BY_RCU and the cleanup is delayed,
  including the directores removal
- __kmem_cache_shutdown() fails due to outstanding objects - the
  directories remain indefinitely

When a cache is recreated with the same name, such as due to module
unload followed by a load, the directories will fail to be recreated for
the new instance of the cache due to the old directories being present.
The cache will also appear twice in /proc/slabinfo.

While we want to convert the SLAB_TYPESAFE_BY_RCU cleanup to be
synchronous again, the second point remains. So let's fix this first and
have the directories and slabinfo removed immediately in
kmem_cache_destroy() and regardless of __kmem_cache_shutdown() success.

This should not make debugging harder if __kmem_cache_shutdown() fails,
because a detailed report of outstanding objects is printed into dmesg
already due to the failure.

Also simplify kmem_cache_release() sysfs handling by using
__is_defined(SLAB_SUPPORTS_SYSFS).

Note the resulting code in kmem_cache_destroy() is a bit ugly but will
be further simplified - this is in order to make small bisectable steps.

Reviewed-by: Jann Horn <jannh@google.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
This commit is contained in:
Vlastimil Babka 2024-08-07 12:31:15 +02:00
parent b5959789e9
commit 4ec10268ed
1 changed files with 26 additions and 31 deletions
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57
mm/slab_common.c
View File

@ -484,31 +484,19 @@ kmem_buckets *kmem_buckets_create(const char *name, slab_flags_t flags,
}
EXPORT_SYMBOL(kmem_buckets_create);
#ifdef SLAB_SUPPORTS_SYSFS
/*
* For a given kmem_cache, kmem_cache_destroy() should only be called
* once or there will be a use-after-free problem. The actual deletion
* and release of the kobject does not need slab_mutex or cpu_hotplug_lock
* protection. So they are now done without holding those locks.
*
* Note that there will be a slight delay in the deletion of sysfs files
* if kmem_cache_release() is called indrectly from a work function.
*/
static void kmem_cache_release(struct kmem_cache *s)
{
if (slab_state >= FULL) {
sysfs_slab_unlink(s);
if (__is_defined(SLAB_SUPPORTS_SYSFS) && slab_state >= FULL)
sysfs_slab_release(s);
} else {
else
slab_kmem_cache_release(s);
}
}
#else
static void kmem_cache_release(struct kmem_cache *s)
{
slab_kmem_cache_release(s);
}
#endif
static void slab_caches_to_rcu_destroy_workfn(struct work_struct *work)
{
@ -534,7 +522,6 @@ static void slab_caches_to_rcu_destroy_workfn(struct work_struct *work)
rcu_barrier();
list_for_each_entry_safe(s, s2, &to_destroy, list) {
debugfs_slab_release(s);
kfence_shutdown_cache(s);
kmem_cache_release(s);
}
@ -549,8 +536,8 @@ void slab_kmem_cache_release(struct kmem_cache *s)
void kmem_cache_destroy(struct kmem_cache *s)
{
int err = -EBUSY;
bool rcu_set;
int err;
if (unlikely(!s) || !kasan_check_byte(s))
return;
@ -558,11 +545,14 @@ void kmem_cache_destroy(struct kmem_cache *s)
cpus_read_lock();
mutex_lock(&slab_mutex);
rcu_set = s->flags & SLAB_TYPESAFE_BY_RCU;
s->refcount--;
if (s->refcount)
goto out_unlock;
if (s->refcount) {
mutex_unlock(&slab_mutex);
cpus_read_unlock();
return;
}
rcu_set = s->flags & SLAB_TYPESAFE_BY_RCU;
/* free asan quarantined objects */
kasan_cache_shutdown(s);
@ -571,24 +561,29 @@ void kmem_cache_destroy(struct kmem_cache *s)
WARN(err, "%s %s: Slab cache still has objects when called from %pS",
__func__, s->name, (void *)_RET_IP_);
if (err)
goto out_unlock;
list_del(&s->list);
if (rcu_set) {
list_add_tail(&s->list, &slab_caches_to_rcu_destroy);
schedule_work(&slab_caches_to_rcu_destroy_work);
} else {
if (!err && !rcu_set)
kfence_shutdown_cache(s);
debugfs_slab_release(s);
}
out_unlock:
mutex_unlock(&slab_mutex);
cpus_read_unlock();
if (!err && !rcu_set)
if (slab_state >= FULL)
sysfs_slab_unlink(s);
debugfs_slab_release(s);
if (err)
return;
if (rcu_set) {
mutex_lock(&slab_mutex);
list_add_tail(&s->list, &slab_caches_to_rcu_destroy);
schedule_work(&slab_caches_to_rcu_destroy_work);
mutex_unlock(&slab_mutex);
} else {
kmem_cache_release(s);
}
}
EXPORT_SYMBOL(kmem_cache_destroy);