cgroup: use restart_syscall() for retries after offline waits in cgroup_subtree_control_write()

After waiting for a child to finish offline,
cgroup_subtree_control_write() jumps up to retry from after the input
parsing and active protection breaking.  This retry makes the
scheduled locking update - removal of cgroup_tree_mutex - more
difficult.  Let's simplify it by returning with restart_syscall() for
retries.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>

1 files changed, 9 insertions, 9 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 250def0694b4..3251cc9070fa 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2535,7 +2535,7 @@ out_finish:
 static int cgroup_subtree_control_write(struct cgroup_subsys_state *dummy_css,
                                         struct cftype *cft, char *buffer)
 {
-        unsigned int enable_req = 0, disable_req = 0, enable, disable;
+        unsigned int enable = 0, disable = 0;
         struct cgroup *cgrp = dummy_css->cgroup, *child;
         struct cgroup_subsys *ss;
         char *tok, *p;
@@ -2554,11 +2554,11 @@ static int cgroup_subtree_control_write(struct cgroup_subsys_state *dummy_css,
                                 continue;
 
                         if (*tok == '+') {
-                                enable_req |= 1 << ssid;
-                                disable_req &= ~(1 << ssid);
+                                enable |= 1 << ssid;
+                                disable &= ~(1 << ssid);
                         } else if (*tok == '-') {
-                                disable_req |= 1 << ssid;
-                                enable_req &= ~(1 << ssid);
+                                disable |= 1 << ssid;
+                                enable &= ~(1 << ssid);
                         } else {
                                 return -EINVAL;
                         }
@@ -2576,9 +2576,6 @@ static int cgroup_subtree_control_write(struct cgroup_subsys_state *dummy_css,
          */
         cgroup_get(cgrp);
         kernfs_break_active_protection(cgrp->control_kn);
-retry:
-        enable = enable_req;
-        disable = disable_req;
 
         mutex_lock(&cgroup_tree_mutex);
 
@@ -2608,7 +2605,9 @@ retry:
                                 schedule();
                                 finish_wait(&child->offline_waitq, &wait);
                                 cgroup_put(child);
-                                goto retry;
+
+                                ret = restart_syscall();
+                                goto out_unbreak;
                         }
 
                         /* unavailable or not enabled on the parent? */
@@ -2692,6 +2691,7 @@ out_unlock:
         mutex_unlock(&cgroup_mutex);
 out_unlock_tree:
         mutex_unlock(&cgroup_tree_mutex);
+out_unbreak:
         kernfs_unbreak_active_protection(cgrp->control_kn);
         cgroup_put(cgrp);
         return ret;