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Subject[PATCH 1/4] cgroup: change locking order in attach_task_by_pid()
Date
From: Tejun Heo <tj@kernel.org>

cgroup_mutex is updated to nest inside threadgroup_fork_lock instead
of the other way around. threadgroup locking is scheduled to be
updated to cover all threadgroup altering operations and nesting it
inside cgroup_mutex complicates locking dependency unnecessarily.
This also simplifies code a bit.

The ugly "if (threadgroup)" conditionals for threadgroup locking will
soon be removed.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Paul Menage <menage@google.com>
Cc: Li Zefan <lizf@cn.fujitsu.com>
---
kernel/cgroup.c | 22 ++++++++++------------
1 files changed, 10 insertions(+), 12 deletions(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 1d2b6ce..bd1fb5f 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2203,15 +2203,11 @@ 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;
-
if (pid) {
rcu_read_lock();
tsk = find_task_by_vpid(pid);
if (!tsk) {
rcu_read_unlock();
- cgroup_unlock();
return -ESRCH;
}
if (threadgroup) {
@@ -2225,7 +2221,6 @@ static int attach_task_by_pid(struct cgroup *cgrp, u64 pid, bool threadgroup)
} else if (tsk->flags & PF_EXITING) {
/* optimization for the single-task-only case */
rcu_read_unlock();
- cgroup_unlock();
return -ESRCH;
}

@@ -2238,7 +2233,6 @@ static int attach_task_by_pid(struct cgroup *cgrp, u64 pid, bool threadgroup)
cred->euid != tcred->uid &&
cred->euid != tcred->suid) {
rcu_read_unlock();
- cgroup_unlock();
return -EACCES;
}
get_task_struct(tsk);
@@ -2251,15 +2245,19 @@ static int attach_task_by_pid(struct cgroup *cgrp, u64 pid, bool threadgroup)
get_task_struct(tsk);
}

- if (threadgroup) {
+ if (threadgroup)
threadgroup_fork_write_lock(tsk);
- ret = cgroup_attach_proc(cgrp, tsk);
- threadgroup_fork_write_unlock(tsk);
- } else {
- ret = cgroup_attach_task(cgrp, tsk);
+ ret = -ENODEV;
+ if (cgroup_lock_live_group(cgrp)) {
+ if (threadgroup)
+ ret = cgroup_attach_proc(cgrp, tsk);
+ else
+ ret = cgroup_attach_task(cgrp, tsk);
+ cgroup_unlock();
}
+ if (threadgroup)
+ threadgroup_fork_write_unlock(tsk);
put_task_struct(tsk);
- cgroup_unlock();
return ret;
}

--
1.7.6


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