linux-kernel - Re: [PATCH-next v2 2/2] scsi: fix iscsi rescan fails to create block device

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Date:   Sun, 29 Jan 2023 22:29:02 -0500
From:   James Bottomley <jejb@...ux.ibm.com>
To:     Yu Kuai <yukuai1@...weicloud.com>,
        Zhong Jinghua <zhongjinghua@...wei.com>,
        gregkh@...uxfoundation.org, martin.petersen@...cle.com,
        hare@...e.de, bvanassche@....org, emilne@...hat.com
Cc:     linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
        yi.zhang@...wei.com, "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH-next v2 2/2] scsi: fix iscsi rescan fails to create
 block device

On Mon, 2023-01-30 at 11:07 +0800, Yu Kuai wrote:
> Hi,
> 
> 在 2023/01/30 1:30, James Bottomley 写道:
> > On Sat, 2023-01-28 at 17:41 +0800, Zhong Jinghua wrote:
> > > This error will cause a warning:
> > > kobject_add_internal failed for block (error: -2 parent:
> > > 1:0:0:1). In the lower version (such as 5.10), there is no
> > > corresponding error handling, continuing to go down will trigger
> > > a kernel panic, so cc stable.
> > 
> > Is this is important point and what you're saying is that this only
> > panics on kernels before 5.10 or so because after that it's
> > correctly failed by block device error handling so there's nothing
> > to fix in later kernels?
> > 
> > In that case, isn't the correct fix to look at backporting the
> > block device error handling:
> 
> This is the last commit that support error handling, and there are
> many relied patches, and there are lots of refactor in block layer.
> It's not a good idea to backport error handling to lower version.
> 
> Althrough error handling can prevent kernel crash in this case, I
> still think it make sense to make sure kobject is deleted in order,
> parent should not be deleted before child.

Well, look, you've created a very artificial situation where a create
closely followed by a delete of the underlying sdev races with the
create of the block gendisk devices of sd that bind asynchronously to
the created sdev.  The asynchronous nature of the bind gives the
elongated race window so the only real fix is some sort of check that
the sdev is still viable by the time the bind occurs ... probably in
sd_probe(), say a scsi_device_get of sdp at the top which would ensure
viability of the sdev for the entire bind or fail the probe if the sdev
can't be got.

James