Since cgroup_attach_proc is protected by a threadgroup_lock, we no longer need a tasklist_lock to protect while_each_thread. To keep the complexity of the double-check locking in one place, I also moved the thread_group_leader check up into attach_task_by_pid. While at it, also converted a couple of returns to gotos. The suggestion was made here: https://lkml.org/lkml/2011/12/22/86 Suggested-by: Frederic Weisbecker <fweisbec@xxxxxxxxx> Signed-off-by: Mandeep Singh Baines <msb@xxxxxxxxxxxx> Cc: Tejun Heo <tj@xxxxxxxxxx> Cc: Li Zefan <lizf@xxxxxxxxxxxxxx> Cc: containers@xxxxxxxxxxxxxxxxxxxxxxxxxx Cc: cgroups@xxxxxxxxxxxxxxx Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> Cc: Oleg Nesterov <oleg@xxxxxxxxxx> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Paul Menage <paul@xxxxxxxxxxxxxx> --- kernel/cgroup.c | 52 +++++++++++++++++++++------------------------------- 1 files changed, 21 insertions(+), 31 deletions(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 1042b3c..032139d 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -2102,21 +2102,6 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) if (retval) goto out_free_group_list; - /* prevent changes to the threadgroup list while we take a snapshot. */ - read_lock(&tasklist_lock); - if (!thread_group_leader(leader)) { - /* - * a race with de_thread from another thread's exec() may strip - * us of our leadership, making while_each_thread unsafe to use - * on this task. if this happens, there is no choice but to - * throw this task away and try again (from cgroup_procs_write); - * this is "double-double-toil-and-trouble-check locking". - */ - read_unlock(&tasklist_lock); - retval = -EAGAIN; - goto out_free_group_list; - } - tsk = leader; i = 0; do { @@ -2145,7 +2130,6 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) group_size = i; tset.tc_array = group; tset.tc_array_len = group_size; - read_unlock(&tasklist_lock); /* methods shouldn't be called if no task is actually migrating */ retval = 0; @@ -2247,18 +2231,12 @@ static int attach_task_by_pid(struct cgroup *cgrp, u64 pid, bool threadgroup) tsk = find_task_by_vpid(pid); if (!tsk) { rcu_read_unlock(); - cgroup_unlock(); - return -ESRCH; + ret= -ESRCH; + goto out_unlock_cgroup; } - if (threadgroup) { - /* - * RCU protects this access, since tsk was found in the - * tid map. a race with de_thread may cause group_leader - * to stop being the leader, but cgroup_attach_proc will - * detect it later. - */ + /* we check later for a group_leader race with de_thread */ + if (threadgroup) tsk = tsk->group_leader; - } /* * even if we're attaching all tasks in the thread group, we * only need to check permissions on one of them. @@ -2268,8 +2246,8 @@ 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; + ret = -EACCES; + goto out_unlock_cgroup; } get_task_struct(tsk); rcu_read_unlock(); @@ -2283,14 +2261,26 @@ static int attach_task_by_pid(struct cgroup *cgrp, u64 pid, bool threadgroup) threadgroup_lock(tsk); - if (threadgroup) + if (threadgroup) { + if (!thread_group_leader(tsk)) { + /* + * a race with de_thread from another thread's exec() + * may strip us of our leadership, if this happens, + * there is no choice but to throw this task away and + * try again (from cgroup_procs_write); this is + * "double-double-toil-and-trouble-check locking". + */ + ret = -EAGAIN; + goto out_unlock_threadgroup; + } ret = cgroup_attach_proc(cgrp, tsk); - else + } else ret = cgroup_attach_task(cgrp, tsk); +out_unlock_threadgroup: threadgroup_unlock(tsk); - put_task_struct(tsk); +out_unlock_cgroup: cgroup_unlock(); return ret; } -- 1.7.3.1 _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
