Paul Menage wrote:
> From: Ben Blum <bblum@xxxxxxxxxx>
>
>
> Adds functionality to read/write lock CLONE_THREAD fork()ing per-threadgroup
>
> This patch adds an rwsem that lives in a threadgroup's sighand_struct (next to
> the sighand's atomic count, to piggyback on its cacheline), and two functions
> in kernel/cgroup.c (for now) for easily+safely obtaining and releasing it. If
> another part of the kernel later wants to use such a locking mechanism, the
> CONFIG_CGROUPS ifdefs should be changed to a higher-up flag that CGROUPS and
> the other system would both depend on, and the lock/unlock functions could be
> moved to sched.c or so.
>
> Signed-off-by: Ben Blum <bblum@xxxxxxxxxx>
> Signed-off-by: Paul Menage <menage@xxxxxxxxxx>
>
Looks fine to me.
Acked-by: Li Zefan <lizf@xxxxxxxxxxxxxx>
...
> +struct sighand_struct *threadgroup_fork_lock(struct task_struct *tsk)
> +{
> + struct sighand_struct *sighand;
> + struct task_struct *p;
> +
> + /* tasklist lock protects sighand_struct's disappearance in exit(). */
> + read_lock(&tasklist_lock);
> + if (likely(tsk->sighand)) {
> + /* simple case - check the thread we were given first */
> + sighand = tsk->sighand;
> + } else {
> + sighand = NULL;
> + /*
> + * tsk is exiting; try to find another thread in the group
> + * whose sighand pointer is still alive.
> + */
> + rcu_read_lock();
since we are holding tasklist_lock, I think we don't need to
take rcu lock?
> + list_for_each_entry_rcu(p, &tsk->thread_group, thread_group) {
> + if (p->sighand) {
> + sighand = tsk->sighand;
s/tsk->sighand/p->sighand
> + break;
> + }
> + }
> + rcu_read_unlock();
> + }
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