After the preparation work done in earlier patches, the cgroup_lock can
be trivially replaced with a memcg-specific lock. This is an automatic
translation in every site the values involved were queried.
The sites were values are written, however, used to be naturally called
under cgroup_lock. This is the case for instance of the css_online
callback. For those, we now need to explicitly add the memcg_lock.
Also, now that the memcg_mutex is available, there is no need to abuse
the set_limit mutex in kmemcg value setting. The memcg_mutex will do a
better job, and we now resort to it.
With this, all the calls to cgroup_lock outside cgroup core are gone.
Signed-off-by: Glauber Costa <glommer@xxxxxxxxxxxxx>
---
mm/memcontrol.c | 52 ++++++++++++++++++++++++++++------------------------
1 file changed, 28 insertions(+), 24 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 6d3ad21..d3b78b9 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -470,6 +470,13 @@ enum res_type {
#define MEM_CGROUP_RECLAIM_SHRINK_BIT 0x1
#define MEM_CGROUP_RECLAIM_SHRINK (1 << MEM_CGROUP_RECLAIM_SHRINK_BIT)
+/*
+ * The memcg mutex needs to be held for any globally visible cgroup change.
+ * Group creation and tunable propagation, as well as any change that depends
+ * on the tunables being in a consistent state.
+ */
+static DEFINE_MUTEX(memcg_mutex);
+
static void mem_cgroup_get(struct mem_cgroup *memcg);
static void mem_cgroup_put(struct mem_cgroup *memcg);
@@ -2902,7 +2909,7 @@ int memcg_cache_id(struct mem_cgroup *memcg)
* operation, because that is its main call site.
*
* But when we create a new cache, we can call this as well if its parent
- * is kmem-limited. That will have to hold set_limit_mutex as well.
+ * is kmem-limited. That will have to hold memcg_mutex as well.
*/
int memcg_update_cache_sizes(struct mem_cgroup *memcg)
{
@@ -2917,7 +2924,7 @@ int memcg_update_cache_sizes(struct mem_cgroup *memcg)
* the beginning of this conditional), is no longer 0. This
* guarantees only one process will set the following boolean
* to true. We don't need test_and_set because we're protected
- * by the set_limit_mutex anyway.
+ * by the memcg_mutex anyway.
*/
memcg_kmem_set_activated(memcg);
@@ -3258,9 +3265,9 @@ void kmem_cache_destroy_memcg_children(struct kmem_cache *s)
*
* Still, we don't want anyone else freeing memcg_caches under our
* noses, which can happen if a new memcg comes to life. As usual,
- * we'll take the set_limit_mutex to protect ourselves against this.
+ * we'll take the memcg_mutex to protect ourselves against this.
*/
- mutex_lock(&set_limit_mutex);
+ mutex_lock(&memcg_mutex);
for (i = 0; i < memcg_limited_groups_array_size; i++) {
c = s->memcg_params->memcg_caches[i];
if (!c)
@@ -3283,7 +3290,7 @@ void kmem_cache_destroy_memcg_children(struct kmem_cache *s)
cancel_work_sync(&c->memcg_params->destroy);
kmem_cache_destroy(c);
}
- mutex_unlock(&set_limit_mutex);
+ mutex_unlock(&memcg_mutex);
}
struct create_work {
@@ -4730,7 +4737,7 @@ static inline bool __memcg_has_children(struct mem_cgroup *memcg)
}
/*
- * must be called with cgroup_lock held, unless the cgroup is guaranteed to be
+ * must be called with memcg_mutex held, unless the cgroup is guaranteed to be
* already dead (like in mem_cgroup_force_empty, for instance). This is
* different than mem_cgroup_count_children, in the sense that we don't really
* care how many children we have, we only need to know if we have any. It is
@@ -4811,7 +4818,7 @@ static int mem_cgroup_hierarchy_write(struct cgroup *cont, struct cftype *cft,
if (parent)
parent_memcg = mem_cgroup_from_cont(parent);
- cgroup_lock();
+ mutex_lock(&memcg_mutex);
if (memcg->use_hierarchy == val)
goto out;
@@ -4834,7 +4841,7 @@ static int mem_cgroup_hierarchy_write(struct cgroup *cont, struct cftype *cft,
retval = -EINVAL;
out:
- cgroup_unlock();
+ mutex_unlock(&memcg_mutex);
return retval;
}
@@ -4934,14 +4941,10 @@ static int memcg_update_kmem_limit(struct cgroup *cont, u64 val)
* After it first became limited, changes in the value of the limit are
* of course permitted.
*
- * Taking the cgroup_lock is really offensive, but it is so far the only
- * way to guarantee that no children will appear. There are plenty of
- * other offenders, and they should all go away. Fine grained locking
- * is probably the way to go here. When we are fully hierarchical, we
- * can also get rid of the use_hierarchy check.
+ * We are protected by the memcg_mutex, so no other cgroups can appear
+ * in the mean time.
*/
- cgroup_lock();
- mutex_lock(&set_limit_mutex);
+ mutex_lock(&memcg_mutex);
if (!memcg->kmem_account_flags && val != RESOURCE_MAX) {
if (cgroup_task_count(cont) || memcg_has_children(memcg)) {
ret = -EBUSY;
@@ -4966,8 +4969,7 @@ static int memcg_update_kmem_limit(struct cgroup *cont, u64 val)
} else
ret = res_counter_set_limit(&memcg->kmem, val);
out:
- mutex_unlock(&set_limit_mutex);
- cgroup_unlock();
+ mutex_unlock(&memcg_mutex);
/*
* We are by now familiar with the fact that we can't inc the static
@@ -5024,9 +5026,9 @@ static int memcg_propagate_kmem(struct mem_cgroup *memcg)
mem_cgroup_get(memcg);
static_key_slow_inc(&memcg_kmem_enabled_key);
- mutex_lock(&set_limit_mutex);
+ mutex_lock(&memcg_mutex);
ret = memcg_update_cache_sizes(memcg);
- mutex_unlock(&set_limit_mutex);
+ mutex_unlock(&memcg_mutex);
#endif
out:
return ret;
@@ -5356,17 +5358,17 @@ static int mem_cgroup_swappiness_write(struct cgroup *cgrp, struct cftype *cft,
parent = mem_cgroup_from_cont(cgrp->parent);
- cgroup_lock();
+ mutex_lock(&memcg_mutex);
/* If under hierarchy, only empty-root can set this value */
if ((parent->use_hierarchy) || memcg_has_children(memcg)) {
- cgroup_unlock();
+ mutex_unlock(&memcg_mutex);
return -EINVAL;
}
memcg->swappiness = val;
- cgroup_unlock();
+ mutex_unlock(&memcg_mutex);
return 0;
}
@@ -5692,7 +5694,7 @@ static int mem_cgroup_oom_control_write(struct cgroup *cgrp,
parent = mem_cgroup_from_cont(cgrp->parent);
- cgroup_lock();
+ mutex_lock(&memcg_mutex);
/* oom-kill-disable is a flag for subhierarchy. */
if ((parent->use_hierarchy) ||
(memcg->use_hierarchy && !list_empty(&cgrp->children))) {
@@ -5702,7 +5704,7 @@ static int mem_cgroup_oom_control_write(struct cgroup *cgrp,
memcg->oom_kill_disable = val;
if (!val)
memcg_oom_recover(memcg);
- cgroup_unlock();
+ mutex_unlock(&memcg_mutex);
return 0;
}
@@ -6140,6 +6142,7 @@ mem_cgroup_css_online(struct cgroup *cont)
if (!cont->parent)
return 0;
+ mutex_lock(&memcg_mutex);
memcg = mem_cgroup_from_cont(cont);
parent = mem_cgroup_from_cont(cont->parent);
@@ -6173,6 +6176,7 @@ mem_cgroup_css_online(struct cgroup *cont)
}
error = memcg_init_kmem(memcg, &mem_cgroup_subsys);
+ mutex_unlock(&memcg_mutex);
if (error) {
/*
* We call put now because our (and parent's) refcnts
--
1.8.1
--
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