linux-kernel - Re: [PATCH v2] block: Skip destroyed blkg when restart in blkg_destroy

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Date:   Fri, 28 Apr 2023 14:49:53 +0800
From:   Tao Su <tao1.su@...ux.intel.com>
To:     Yu Kuai <yukuai1@...weicloud.com>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        tj@...nel.org, josef@...icpanda.com, axboe@...nel.dk,
        "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH v2] block: Skip destroyed blkg when restart in
 blkg_destroy_all()

On Fri, Apr 28, 2023 at 02:12:06PM +0800, Yu Kuai wrote:
> Hi,
> 
> 在 2023/04/28 12:51, Tao Su 写道:
> > Kernel hang in blkg_destroy_all() when total blkg greater than
> > BLKG_DESTROY_BATCH_SIZE, because of not removing destroyed blkg in
> > blkg_list. So the size of blkg_list is same after destroying a
> > batch of blkg, and the infinite 'restart' occurs.
> > 
> > Since blkg should stay on the queue list until blkg_free_workfn(),
> > skip destroyed blkg when restart a new round, which will solve this
> > kernel hang issue and satisfy the previous will to restart.
> 
> Please add a fix tag:
> 
> Fixes: f1c006f1c685 ("blk-cgroup: synchronize pd_free_fn() from
> blkg_free_workfn() and blkcg_deactivate_policy()")
> > 
> > Reported-by: Xiangfei Ma <xiangfeix.ma@...el.com>
> > Tested-by: Xiangfei Ma <xiangfeix.ma@...el.com>
> > Tested-by: Farrah Chen <farrah.chen@...el.com>
> > Signed-off-by: Yu Kuai <yukuai1@...weicloud.com>
> 
> You can remove this tag, and feel free to add:
> 
> Suggested-and-reviewed-by: Yu Kuai <yukuai3@...wei.com>

Got it, thanks!

Tao

> 
> Thanks,
> Kuai
> > Signed-off-by: Tao Su <tao1.su@...ux.intel.com>
> > ---
> > v2:
> > - change 'directly remove destroyed blkg' to 'skip destroyed blkg'
> > 
> > v1:
> > - https://lore.kernel.org/all/20230425075911.839539-1-tao1.su@linux.intel.com/
> > 
> >   block/blk-cgroup.c | 3 +++
> >   1 file changed, 3 insertions(+)
> > 
> > diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
> > index bd50b55bdb61..75bad5d60c9f 100644
> > --- a/block/blk-cgroup.c
> > +++ b/block/blk-cgroup.c
> > @@ -528,6 +528,9 @@ static void blkg_destroy_all(struct gendisk *disk)
> >   	list_for_each_entry_safe(blkg, n, &q->blkg_list, q_node) {
> >   		struct blkcg *blkcg = blkg->blkcg;
> > +		if (hlist_unhashed(&blkg->blkcg_node))
> > +			continue;
> > +
> >   		spin_lock(&blkcg->lock);
> >   		blkg_destroy(blkg);
> >   		spin_unlock(&blkcg->lock);
> > 
>