memcg: cgroup_write_event_control() now knows @css is for memcg

@css for cgroup_write_event_control() is now always for memcg and the
target file should be a memcg file too.  Drop code which assumes @css
is dummy_css and the target file may belong to different subsystems.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

1 files changed, 11 insertions, 16 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 02dae3292668..d00368110b08 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6056,10 +6056,10 @@ static void cgroup_event_ptable_queue_proc(struct file *file,
  * Input must be in format '<event_fd> <control_fd> <args>'.
  * Interpretation of args is defined by control file implementation.
  */
-static int cgroup_write_event_control(struct cgroup_subsys_state *dummy_css,
+static int cgroup_write_event_control(struct cgroup_subsys_state *css,
                                       struct cftype *cft, const char *buffer)
 {
-        struct cgroup *cgrp = dummy_css->cgroup;
+        struct cgroup *cgrp = css->cgroup;
         struct cgroup_event *event;
         struct cgroup_subsys_state *cfile_css;
         unsigned int efd, cfd;
@@ -6082,6 +6082,7 @@ static int cgroup_write_event_control(struct cgroup_subsys_state *dummy_css,
         if (!event)
                 return -ENOMEM;
 
+        event->css = css;
         INIT_LIST_HEAD(&event->list);
         init_poll_funcptr(&event->pt, cgroup_event_ptable_queue_proc);
         init_waitqueue_func_entry(&event->wait, cgroup_event_wake);
@@ -6117,23 +6118,17 @@ static int cgroup_write_event_control(struct cgroup_subsys_state *dummy_css,
                 goto out_put_cfile;
         }
 
-        if (!event->cft->ss) {
-                ret = -EBADF;
-                goto out_put_cfile;
-        }
-
         /*
-         * Determine the css of @cfile, verify it belongs to the same
-         * cgroup as cgroup.event_control, and associate @event with it.
-         * Remaining events are automatically removed on cgroup destruction
-         * but the removal is asynchronous, so take an extra ref.
+         * Verify @cfile should belong to @css.  Also, remaining events are
+         * automatically removed on cgroup destruction but the removal is
+         * asynchronous, so take an extra ref on @css.
          */
         rcu_read_lock();
 
         ret = -EINVAL;
-        event->css = cgroup_css(cgrp, event->cft->ss);
-        cfile_css = css_from_dir(cfile.file->f_dentry->d_parent, event->cft->ss);
-        if (event->css && event->css == cfile_css && css_tryget(event->css))
+        cfile_css = css_from_dir(cfile.file->f_dentry->d_parent,
+                                 &mem_cgroup_subsys);
+        if (cfile_css == css && css_tryget(css))
                 ret = 0;
 
         rcu_read_unlock();
@@ -6145,7 +6140,7 @@ static int cgroup_write_event_control(struct cgroup_subsys_state *dummy_css,
                 goto out_put_css;
         }
 
-        ret = event->cft->register_event(event->css, event->cft,
+        ret = event->cft->register_event(css, event->cft,
                         event->eventfd, buffer);
         if (ret)
                 goto out_put_css;
@@ -6162,7 +6157,7 @@ static int cgroup_write_event_control(struct cgroup_subsys_state *dummy_css,
         return 0;
 
 out_put_css:
-        css_put(event->css);
+        css_put(css);
 out_put_cfile:
         fdput(cfile);
 out_put_eventfd: