vmpressure: make sure there are no events queued after memcg is offlined

vmpressure is called synchronously from reclaim where the target_memcg
is guaranteed to be alive but the eventfd is signaled from the work
queue context.  This means that memcg (along with vmpressure structure
which is embedded into it) might go away while the work item is pending
which would result in use-after-release bug.

We have two possible ways how to fix this.  Either vmpressure pins memcg
before it schedules vmpr->work and unpin it in vmpressure_work_fn or
explicitely flush the work item from the css_offline context (as
suggested by Tejun).

This patch implements the later one and it introduces vmpressure_cleanup
which flushes the vmpressure work queue item item.  It hooks into
mem_cgroup_css_offline after the memcg itself is cleaned up.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Michal Hocko <mhocko@suse.cz>
Reported-by: Tejun Heo <tj@kernel.org>
Cc: Anton Vorontsov <anton.vorontsov@linaro.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Li Zefan <lizefan@huawei.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/vmpressure.h b/include/linux/vmpressure.h
index 2081680e015d746c18aa0765265bbe2106ded6d4..7dc17e2456de141ef3241a73af02fbec9b9c1ee5 100644 (file)
--- a/include/linux/vmpressure.h
+++ b/include/linux/vmpressure.h
@@ -30,6 +30,7 @@ extern void vmpressure(gfp_t gfp, struct mem_cgroup *memcg,
 extern void vmpressure_prio(gfp_t gfp, struct mem_cgroup *memcg, int prio);
 
 extern void vmpressure_init(struct vmpressure *vmpr);
+extern void vmpressure_cleanup(struct vmpressure *vmpr);
 extern struct vmpressure *memcg_to_vmpressure(struct mem_cgroup *memcg);
 extern struct cgroup_subsys_state *vmpressure_to_css(struct vmpressure *vmpr);
 extern struct vmpressure *css_to_vmpressure(struct cgroup_subsys_state *css);

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 00a7a664b9c16b92769f98fec8117e7c712e6ab1..c290a1cf38624adf8372d67ccf60d9ec01ff1357 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6335,6 +6335,7 @@ static void mem_cgroup_css_offline(struct cgroup *cont)
        mem_cgroup_invalidate_reclaim_iterators(memcg);
        mem_cgroup_reparent_charges(memcg);
        mem_cgroup_destroy_all_caches(memcg);
+       vmpressure_cleanup(&memcg->vmpressure);
 }
 
 static void mem_cgroup_css_free(struct cgroup *cont)

diff --git a/mm/vmpressure.c b/mm/vmpressure.c
index 192f9731931da75b24b9a5f9b28203de9a0e2f85..0c1e37d829fa026a9fc61ef93b569087939867c5 100644 (file)
--- a/mm/vmpressure.c
+++ b/mm/vmpressure.c
@@ -372,3 +372,19 @@ void vmpressure_init(struct vmpressure *vmpr)
        INIT_LIST_HEAD(&vmpr->events);
        INIT_WORK(&vmpr->work, vmpressure_work_fn);
 }
+
+/**
+ * vmpressure_cleanup() - shuts down vmpressure control structure
+ * @vmpr:      Structure to be cleaned up
+ *
+ * This function should be called before the structure in which it is
+ * embedded is cleaned up.
+ */
+void vmpressure_cleanup(struct vmpressure *vmpr)
+{
+       /*
+        * Make sure there is no pending work before eventfd infrastructure
+        * goes away.
+        */
+       flush_work(&vmpr->work);
+}