linux-kernel - Re: [PATCH v12 1/3] bio: control bio max size

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Message-ID: <221377e3-05d1-f250-1ad8-6e5c9485d756@acm.org>
Date:   Mon, 7 Jun 2021 09:46:56 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Changheun Lee <nanich.lee@...sung.com>, damien.lemoal@....com,
        Avri.Altman@....com, Johannes.Thumshirn@....com,
        alex_y_xu@...oo.ca, alim.akhtar@...sung.com,
        asml.silence@...il.com, axboe@...nel.dk, bgoncalv@...hat.com,
        cang@...eaurora.org, gregkh@...uxfoundation.org,
        jaegeuk@...nel.org, jejb@...ux.ibm.com, jisoo2146.oh@...sung.com,
        junho89.kim@...sung.com, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
        martin.petersen@...cle.com, ming.lei@...hat.com,
        mj0123.lee@...sung.com, osandov@...com, patchwork-bot@...nel.org,
        seunghwan.hyun@...sung.com, sookwan7.kim@...sung.com,
        tj@...nel.org, tom.leiming@...il.com, woosung2.lee@...sung.com,
        yi.zhang@...hat.com, yt0928.kim@...sung.com
Subject: Re: [PATCH v12 1/3] bio: control bio max size

On 6/6/21 11:35 PM, Christoph Hellwig wrote:
> On Fri, Jun 04, 2021 at 07:52:35AM -0700, Bart Van Assche wrote:
>>  Damien is right. bd_disk can be NULL. From
> 
> bd_disk is initialized in bdev_alloc, so it should never be NULL.
> bi_bdev OTOH is only set afer bio_add_page in various places or not at
> all in case of passthrough bios.  Which is a bit of a mess and I have
> plans to fix it.

Hi Christoph,

Thank you for having shared your plans for how to improve how bi_bdev is
set.

In case you would not yet have had the time to do this, please take a
look at the call trace available on
https://lore.kernel.org/linux-block/20210425043020.30065-1-bvanassche@acm.org/.
That call trace shows how bio_add_pc_page() is called by the SCSI core
before alloc_disk() is called. I think that sending a SCSI command
before alloc_disk() is called is fundamental in the SCSI core because
the SCSI INQUIRY command has to be sent before it is known whether or
not a SCSI LUN represents a disk.

Thanks,

Bart.