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Subject[PATCH v6 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 | 19 +++++++++++++++----
1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 09b26673b63f..2914a8f0aa85 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)
{
@@ -629,6 +630,7 @@ void memcg_create_kmem_cache(struct mem_cgroup *memcg,
struct memcg_cache_array *arr;
struct kmem_cache *s = NULL;
char *cache_name;
+ bool dying;
int idx;

get_online_cpus();
@@ -640,7 +642,13 @@ void memcg_create_kmem_cache(struct mem_cgroup *memcg,
* The memory cgroup could have been offlined while the cache
* creation work was pending.
*/
- if (memcg->kmem_state != KMEM_ONLINE || root_cache->memcg_params.dying)
+ if (memcg->kmem_state != KMEM_ONLINE)
+ goto out_unlock;
+
+ spin_lock_irq(&memcg_kmem_wq_lock);
+ dying = root_cache->memcg_params.dying;
+ spin_unlock_irq(&memcg_kmem_wq_lock);
+ if (dying)
goto out_unlock;

idx = memcg_cache_id(memcg);
@@ -735,14 +743,17 @@ static void kmemcg_cache_deactivate(struct kmem_cache *s)

__kmemcg_cache_deactivate(s);

+ 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)
@@ -852,9 +863,9 @@ 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
--
2.20.1
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