linux-kernel - Re: [PATCH v2 1/2] sysfs: handle 'parent deleted before child added'

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Message-ID: <CABE8wwuMyH7nrPZWarWw1Z8=oM_Z4eUcupnsyxA9NF=Y1R_Apw@mail.gmail.com>
Date:	Fri, 6 Apr 2012 14:06:50 -0700
From:	"Williams, Dan J" <dan.j.williams@...el.com>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	James Bottomley <JBottomley@...allels.com>,
	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org
Subject: Re: [PATCH v2 1/2] sysfs: handle 'parent deleted before child added'

On Fri, Apr 6, 2012 at 1:45 PM, Greg KH <gregkh@...uxfoundation.org> wrote:
> On Fri, Apr 06, 2012 at 01:41:06PM -0700, Dan Williams wrote:
>> In scsi at least two cases of the parent device being deleted before the
>> child is added have been observed.
>>
>> 1/ scsi is performing async scans and the device is removed prior to the
>>    async can thread running (can happen with an in-opportune / unlikely
>>    unplug during initial scan).
>
> That sounds like a bug in the scsi code, doesn't it?
>
>> 2/ libsas discovery event running after the parent port has been torn
>>    down (this is a bug in libsas).
>
> Is this fixed somewhere?

Yes, these two issues have pending fixes that are posted to linux-scsi:

http://marc.info/?l=linux-scsi&m=133239707903443&w=2
http://marc.info/?l=linux-scsi&m=133239709603452&w=2

> I don't want to paper over bugs like this by changing the sysfs core.
> We went through this a lot years ago when scsi changed to use the driver
> core, and I thought we had fixed all of these types of errors properly.

Hotplug lifetime rules are still transport specific.  So in this case
scsi-core is innocent these are bugs from libsas and
scsi_transport_sas.

> So, any chance to fix these properly as well?

This patch doesn't really paper over anything.  It turns a NULL
pointer crash into an explicit warning from kobject_add_internal.  For
the libsas/scsi case this device_add() failure is still fatal.
Regardless of whether sysfs changes the above two fixes are still
required.

Since the -EEXIST case is just a KERN_ERR and not a BUG_ON I figured
it was worthwhile to post a patch to do the same for this 'parent
deleted' case.  But if crashing is the expectation then this patch can
be dropped.

--
Dan
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