linux-kernel - Re: [PATCH block/for-next] blk-cgroup: cgroup_rstat

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Message-ID: <6f791736-2728-be53-9544-e0a0f0d09dd0@ti.com>
Date:   Mon, 18 Nov 2019 14:09:40 +0530
From:   Faiz Abbas <faiz_abbas@...com>
To:     Tejun Heo <tj@...nel.org>, Jens Axboe <axboe@...nel.dk>
CC:     <cgroups@...r.kernel.org>, <linux-block@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <lizefan@...wei.com>,
        <hannes@...xchg.org>, <kernel-team@...com>,
        Dan Schatzberg <dschatzberg@...com>, Daniel Xu <dlxu@...com>
Subject: Re: [PATCH block/for-next] blk-cgroup: cgroup_rstat_updated()
 shouldn't be called on cgroup1

Hi,

On 15/11/19 4:01 AM, Tejun Heo wrote:
> Currently, cgroup rstat is supported only on cgroup2 hierarchy and
> rstat functions shouldn't be called on cgroup1 cgroups.  While
> converting blk-cgroup core statistics to rstat, f73316482977
> ("blk-cgroup: reimplement basic IO stats using cgroup rstat")
> accidentally ended up calling cgroup_rstat_updated() on cgroup1
> cgroups causing crashes.
> 
> Longer term, we probably should add cgroup1 support to rstat but for
> now let's mask the call directly.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Fixes: f73316482977 ("blk-cgroup: reimplement basic IO stats using cgroup rstat")
Tested-by: Faiz Abbas <faiz_abbas@...com>
> ---
>  include/linux/blk-cgroup.h |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
> index 48a66738143d..19394c77ed99 100644
> --- a/include/linux/blk-cgroup.h
> +++ b/include/linux/blk-cgroup.h
> @@ -626,7 +626,8 @@ static inline bool blkcg_bio_issue_check(struct request_queue *q,
>  		bis->cur.ios[rwd]++;
>  
>  		u64_stats_update_end(&bis->sync);
> -		cgroup_rstat_updated(blkg->blkcg->css.cgroup, cpu);
> +		if (cgroup_subsys_on_dfl(io_cgrp_subsys))
> +			cgroup_rstat_updated(blkg->blkcg->css.cgroup, cpu);
>  		put_cpu();
>  	}
>  
> 

Thanks,
Faiz