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Subject[PATCH v7 07/10] mm: synchronize access to kmem_cache dying flag using a spinlock
Date
Currently the memcg_params.dying flag and the corresponding
workqueue used for the asynchronous deactivation of kmem_caches
is synchronized using the slab_mutex.

It makes impossible to check this flag from the irq context,
which will be required in order to implement asynchronous release
of kmem_caches.

So let's switch over to the irq-save flavor of the spinlock-based
synchronization.

Signed-off-by: Roman Gushchin <guro@fb.com>
---
mm/slab_common.c | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 9383104651cd..1e5eaf84bf08 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -130,6 +130,7 @@ int __kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t nr,
#ifdef CONFIG_MEMCG_KMEM

LIST_HEAD(slab_root_caches);
+static DEFINE_SPINLOCK(memcg_kmem_wq_lock);

void slab_init_memcg_params(struct kmem_cache *s)
{
@@ -734,14 +735,22 @@ static void kmemcg_cache_deactivate(struct kmem_cache *s)

__kmemcg_cache_deactivate(s);

+ /*
+ * memcg_kmem_wq_lock is used to synchronize memcg_params.dying
+ * flag and make sure that no new kmem_cache deactivation tasks
+ * are queued (see flush_memcg_workqueue() ).
+ */
+ spin_lock_irq(&memcg_kmem_wq_lock);
if (s->memcg_params.root_cache->memcg_params.dying)
- return;
+ goto unlock;

/* pin memcg so that @s doesn't get destroyed in the middle */
css_get(&s->memcg_params.memcg->css);

s->memcg_params.work_fn = __kmemcg_cache_deactivate_after_rcu;
call_rcu(&s->memcg_params.rcu_head, kmemcg_rcufn);
+unlock:
+ spin_unlock_irq(&memcg_kmem_wq_lock);
}

void memcg_deactivate_kmem_caches(struct mem_cgroup *memcg)
@@ -851,9 +860,9 @@ static int shutdown_memcg_caches(struct kmem_cache *s)

static void flush_memcg_workqueue(struct kmem_cache *s)
{
- mutex_lock(&slab_mutex);
+ spin_lock_irq(&memcg_kmem_wq_lock);
s->memcg_params.dying = true;
- mutex_unlock(&slab_mutex);
+ spin_unlock_irq(&memcg_kmem_wq_lock);

/*
* SLAB and SLUB deactivate the kmem_caches through call_rcu. Make
--
2.21.0
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