Re: [PATCH 01/10] blk-cgroup: use cgroup lock and rcu to protect iterating blkcg blkgs

[Yu Kuai]

Hi,

在 2025/09/26 1:07, Yu Kuai 写道:
> Hi,
>
> 在 2025/9/25 23:57, Bart Van Assche 写道:
> > On 9/25/25 1:15 AM, Yu Kuai wrote:
> > > It's safe to iterate blkgs with cgroup lock or rcu lock held, prevent
> > > nested queue_lock under rcu lock, and prepare to convert protecting
> > > blkcg with blkcg_mutex instead of queuelock.
> >
> > Iterating blkgs without holding q->queue_lock is safe but accessing the
> > blkg members without holding that lock is not safe since q->queue_lock
> > is acquired by all code that modifies blkg members. Should perhaps a new
> > spinlock be introduced to serialize blkg modifications?

Actually, only blkcg_print_blkgs() is using rcu in this patch, and take
a look at the callers, I don't see anyone have to hold queue_lock. Can
you explain in detail which field from blkg is problematic in this
patch?

Thanks,
Kuai

> >
> No need for a new lock, I think blkcg->lock can do that.
>
> Thanks,
> Kuai
>
> > Thanks,
> >
> > Bart.
> .