linux-kernel - Re: [PATCH 2/4] blkcg: Restructure blkg_conf

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Message-ID: <Y72vjbufcqtRdl2C@slm.duckdns.org>
Date:   Tue, 10 Jan 2023 08:33:49 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Christoph Hellwig <hch@....de>
Cc:     axboe@...nel.dk, josef@...icpanda.com, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] blkcg: Restructure blkg_conf_prep() and friends

On Tue, Jan 10, 2023 at 08:09:29AM +0100, Christoph Hellwig wrote:
> On Thu, Jan 05, 2023 at 11:24:30AM -1000, Tejun Heo wrote:
> > * blkg_conf_open_bdev() is updated to take a pointer to blkg_conf_ctx like
> >   blkg_conf_prep() and can be called multiple times safely. Instead of
> >   modifying the double pointer to input string directly,
> >   blkg_conf_open_bdev() now sets blkg_conf_ctx->body.
> 
> This looks pretty awkward for the externals callers of blkcg_conf_open_bdev
> in blk-iocost.  I'd either keep the calling conventions as they are
> at the moment, or just open code blkcg_conf_open_bdev in blk-iocost.

Because we're coming in from cgroupfs, we aren't synchronizing properly
against blkdevs going away. For all config attempt coming in from cgroup
side, we'll need to synchronize explicitly and these config helper blocks
look like a good place to do so. Please take a look at the thread with Yu
Kuai. Imma update the comment to include that but yeah let's keep it this
way for that.

Thanks.

-- 
tejun