path: root/kernel/fork.c
diff options
authorTejun Heo <>2012-10-16 15:03:14 -0700
committerTejun Heo <>2012-10-16 15:03:14 -0700
commit5edee61edeaaebafe584f8fb7074c1ef4658596b (patch)
tree23e6ee3581eb0009b3c2a2686c25fdba538219de /kernel/fork.c
parentddffeb8c4d0331609ef2581d84de4d763607bd37 (diff)
cgroup: cgroup_subsys->fork() should be called after the task is added to css_set
cgroup core has a bug which violates a basic rule about event notifications - when a new entity needs to be added, you add that to the notification list first and then make the new entity conform to the current state. If done in the reverse order, an event happening inbetween will be lost. cgroup_subsys->fork() is invoked way before the new task is added to the css_set. Currently, cgroup_freezer is the only user of ->fork() and uses it to make new tasks conform to the current state of the freezer. If FROZEN state is requested while fork is in progress between cgroup_fork_callbacks() and cgroup_post_fork(), the child could escape freezing - the cgroup isn't frozen when ->fork() is called and the freezer couldn't see the new task on the css_set. This patch moves cgroup_subsys->fork() invocation to cgroup_post_fork() after the new task is added to the css_set. cgroup_fork_callbacks() is removed. Because now a task may be migrated during cgroup_subsys->fork(), freezer_fork() is updated so that it adheres to the usual RCU locking and the rather pointless comment on why locking can be different there is removed (if it doesn't make anything simpler, why even bother?). Signed-off-by: Tejun Heo <> Cc: Oleg Nesterov <> Cc: Rafael J. Wysocki <> Cc:
Diffstat (limited to 'kernel/fork.c')
1 files changed, 1 insertions, 8 deletions
diff --git a/kernel/fork.c b/kernel/fork.c
index 8b20ab7d3aa2..acc4cb62f32f 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1135,7 +1135,6 @@ static struct task_struct *copy_process(unsigned long clone_flags,
int retval;
struct task_struct *p;
- int cgroup_callbacks_done = 0;
if ((clone_flags & (CLONE_NEWNS|CLONE_FS)) == (CLONE_NEWNS|CLONE_FS))
return ERR_PTR(-EINVAL);
@@ -1393,12 +1392,6 @@ static struct task_struct *copy_process(unsigned long clone_flags,
p->task_works = NULL;
- /* Now that the task is set up, run cgroup callbacks if
- * necessary. We need to run them before the task is visible
- * on the tasklist. */
- cgroup_fork_callbacks(p);
- cgroup_callbacks_done = 1;
/* Need tasklist lock for parent etc handling! */
@@ -1503,7 +1496,7 @@ bad_fork_cleanup_cgroup:
if (clone_flags & CLONE_THREAD)
- cgroup_exit(p, cgroup_callbacks_done);
+ cgroup_exit(p, 0);