It doesn't make sense to nest cgroup_mutex inside threadgroup_lock
when it should be outer to most all locks used by all cgroup
controllers. It was nested inside threadgroup_lock only because some
controllers were abusing cgroup_mutex inside controllers leading to
locking order inversion.
cgroup_mutex is no longer abused by controllers and can be put outer
to threadgroup_lock. Reverse the locking order in
attach_task_by_pid().
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Cc: Li Zefan <lizefan@xxxxxxxxxx>
---
Li, can you please ack this?
Thanks!
kernel/cgroup.c | 21 ++++++++-------------
1 file changed, 8 insertions(+), 13 deletions(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 04fa2ab..24106b8 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2134,17 +2134,13 @@ static int attach_task_by_pid(struct cgroup *cgrp, u64 pid, bool threadgroup)
const struct cred *cred = current_cred(), *tcred;
int ret;
- if (!cgroup_lock_live_group(cgrp))
- return -ENODEV;
-
retry_find_task:
rcu_read_lock();
if (pid) {
tsk = find_task_by_vpid(pid);
if (!tsk) {
rcu_read_unlock();
- ret= -ESRCH;
- goto out_unlock_cgroup;
+ return -ESRCH;
}
/*
* even if we're attaching all tasks in the thread group, we
@@ -2155,8 +2151,7 @@ retry_find_task:
!uid_eq(cred->euid, tcred->uid) &&
!uid_eq(cred->euid, tcred->suid)) {
rcu_read_unlock();
- ret = -EACCES;
- goto out_unlock_cgroup;
+ return -EACCES;
}
} else
tsk = current;
@@ -2170,9 +2165,8 @@ retry_find_task:
* with no rt_runtime allocated. Just say no.
*/
if (tsk == kthreadd_task || (tsk->flags & PF_THREAD_BOUND)) {
- ret = -EINVAL;
rcu_read_unlock();
- goto out_unlock_cgroup;
+ return -EINVAL;
}
get_task_struct(tsk);
@@ -2194,13 +2188,14 @@ retry_find_task:
}
}
- ret = cgroup_attach_task(cgrp, tsk, threadgroup);
+ ret = -ENODEV;
+ if (cgroup_lock_live_group(cgrp)) {
+ ret = cgroup_attach_task(cgrp, tsk, threadgroup);
+ cgroup_unlock();
+ }
threadgroup_unlock(tsk);
-
put_task_struct(tsk);
-out_unlock_cgroup:
- cgroup_unlock();
return ret;
}
--
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