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

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Message-ID: <20120406211711.GA12075@kroah.com>
Date:	Fri, 6 Apr 2012 14:17:11 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	"Williams, Dan J" <dan.j.williams@...el.com>
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 06, 2012 at 02:06:50PM -0700, Williams, Dan J wrote:
> 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.

Ok, thanks for the explaination.

> > 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.

No, crashing is not the expectation :)

But, without that crash, would the above fixes ever have been noticed
and fixed?  The device_add() most likely would have quietly failed and
no one would have been the wiser.

Or would something else have caused this to be an obvious problem?

thanks,

greg k-h
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