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

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On Fri, Apr 6, 2012 at 1:45 PM, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> 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:

> 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

> 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

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.

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