linux-kernel - Re: [RFC v2 1/5] zram: remove zram_page_end

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Message-ID: <ZBwrfT8TA5GC5+RH@infradead.org>
Date:   Thu, 23 Mar 2023 03:35:41 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Pankaj Raghav <p.raghav@...sung.com>
Cc:     senozhatsky@...omium.org, viro@...iv.linux.org.uk, axboe@...nel.dk,
        willy@...radead.org, brauner@...nel.org, akpm@...ux-foundation.org,
        minchan@...nel.org, hubcap@...ibond.com, martin@...ibond.com,
        mcgrof@...nel.org, devel@...ts.orangefs.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-block@...r.kernel.org, gost.dev@...sung.com
Subject: Re: [RFC v2 1/5] zram: remove zram_page_end_io function

On Wed, Mar 22, 2023 at 02:50:09PM +0100, Pankaj Raghav wrote:
> -	if (!parent)
> -		bio->bi_end_io = zram_page_end_io;
> -	else
> +	if (parent)

I don't think a non-chained bio without and end_io handler can work.
This !parent case seems to come from writeback_store, and as far as
I can tell is broken already in the current code as it just fires
off an async read without ever waiting for it, using an on-stack bio
just to make things complicated.

The bvec reading code in zram is a mess, but I have an idea how
to clean it up with a little series that should also help with
this issue.