linux-kernel - Re: [PATCH v2] fs-writeback: writeback_sb_inodes：Recalculate 'wrote' according skipped pages

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Date:   Mon, 18 Apr 2022 17:19:37 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Zhihao Cheng <chengzhihao1@...wei.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@....de>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        yukuai3@...wei.com
Subject: Re: [PATCH v2] fs-writeback: writeback_sb_inodes：Recalculate 'wrote' according skipped pages

On Mon, Apr 18, 2022 at 3:12 PM Jens Axboe <axboe@...nel.dk> wrote:
>
> Hmm yes. But doesn't preemption imply a full barrier? As long as we
> assign the plug at the end, we should be fine. And just now looking that
> up, there's even already a comment to that effect in blk_start_plug().
> So barring any weirdness with that, maybe that's the solution.

My worry is more about the code that adds new cb_list entries to the
plug, racing with then some random preemption event that flushes the
plug.

preemption itself is perfectly fine wrt any per-thread data updates
etc, but if preemption then also *changes* the data that is updated,
that's not great.

So that worries me.

             Linus