We can replace the tasklist_lock in cgroup_attach_proc with an rcu_read_lock. Changes in V4: * https://lkml.org/lkml/2011/12/23/284 (Frederic Weisbecker) * Minimize size of rcu_read_lock critical section * Add comment * https://lkml.org/lkml/2011/12/26/136 (Li Zefan) * Split into two patches Changes in V3: * https://lkml.org/lkml/2011/12/22/419 (Frederic Weisbecker) * Add an rcu_read_lock to protect against exit Changes in V2: * https://lkml.org/lkml/2011/12/22/86 (Tejun Heo) * Use a goto instead of returning -EAGAIN 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 | 10 +++++++--- 1 files changed, 7 insertions(+), 3 deletions(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 09867eb..354c539 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -2102,10 +2102,14 @@ 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); tsk = leader; i = 0; + /* + * Prevent freeing of tasks while we take a snapshot. Tasks that are + * already PF_EXITING could be freed from underneath us unless we + * take an rcu_read_lock. + */ + rcu_read_lock(); do { struct task_and_cgroup ent; @@ -2128,11 +2132,11 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader) BUG_ON(retval != 0); i++; } while_each_thread(leader, tsk); + rcu_read_unlock(); /* remember the number of threads in the array for later. */ 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; -- 1.7.3.1 _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
