On Thu, Dec 22, 2011 at 04:57:51PM -0800, Mandeep Singh Baines wrote: > 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); You still need rcu_read_lock()/rcu_read_unlock() around do { } while_each_thread() because threadgroup_lock() doesn't lock the part that remove a thread from its group on exit. _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
