linux-kernel - Re: [PATCH v2 1/5] zram: always chain bio to the parent in read_from_bdev

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Date:   Tue, 4 Apr 2023 12:31:31 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Pankaj Raghav <p.raghav@...sung.com>, axboe@...nel.dk,
        minchan@...nel.org, martin@...ibond.com, hubcap@...ibond.com,
        brauner@...nel.org, viro@...iv.linux.org.uk,
        senozhatsky@...omium.org, willy@...radead.org, hch@....de,
        devel@...ts.orangefs.org, mcgrof@...nel.org,
        linux-block@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, gost.dev@...sung.com,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v2 1/5] zram: always chain bio to the parent in
 read_from_bdev_async

On Tue, 4 Apr 2023 08:06:55 -0700 Christoph Hellwig <hch@...radead.org> wrote:

> On Mon, Apr 03, 2023 at 03:22:17PM +0200, Pankaj Raghav wrote:
> > zram_bvec_read() is called with the bio set to NULL only in
> > writeback_store() function. When a writeback is triggered,
> > zram_bvec_read() is called only if ZRAM_WB flag is not set. That will
> > result only calling zram_read_from_zspool() in __zram_bvec_read().
> > 
> > rw_page callback used to call read_from_bdev_async with a NULL parent
> > bio but that has been removed since commit 3222d8c2a7f8
> > ("block: remove ->rw_page").
> > 
> > We can now safely always call bio_chain() as read_from_bdev_async() will
> > be called with a parent bio set. A WARN_ON_ONCE is added if this function
> > is called with parent set to NULL.
> 
> I'm pretty sure this is wrong.

Thanks, I'll drop this v2 series.

>  I've now sent a series to untangle
> and fix up the zram I/O path, which should address the underlying
> issue here.

I can't find that series.

> It will obviously conflict with this patch, so maybe the best thing is
> to get the other page_endio removals into their respective maintainer
> trees, and then just do the final removal of the unused function after
> -rc1.