Re: [Bug] INFO: task hung in hub_activate

From: Greg KH <gregkh@linuxfoundation.org>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Sam Sun <samsun1006219@gmail.com>, Tejun Heo <tj@kernel.org>,
	linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org,
	"xrivendell7@gmail.com" <xrivendell7@gmail.com>,
	hgajjar@de.adit-jv.com, quic_ugoswami@quicinc.com,
	stanley_chang@realtek.com, heikki.krogerus@linux.intel.com
Subject: Re: [Bug] INFO: task hung in hub_activate
Date: Mon, 4 Mar 2024 17:36:19 +0100	[thread overview]
Message-ID: <2024030428-graph-harmful-1597@gregkh> (raw)
In-Reply-To: <e9d710fc-eace-44de-b3cc-1117c3575ef7@rowland.harvard.edu>

On Mon, Mar 04, 2024 at 11:15:24AM -0500, Alan Stern wrote:
> Third, this must be a generic problem.  It will occur any time a sysfs
> attribute callback tries to lock its device while another process is
> trying to unregister that device.
> 
> We faced this sort of problem some years ago when we were worrying
> about "suicidal" attributes -- ones which would unregister their own
> devices.  I don't remember what the fix was or how it worked.  But we
> need something like it here.
> 
> Greg and Tejun, any ideas?  Is it possible somehow for an attribute file 
> to be removed while its callback is still running?

Yes, it's a pain, and I hate it, but I think SCSI does this somehow for
one of their attributes.  I don't remember how at the moment, and I
can't look it up (am traveling), but this should be a good hint.

thanks,

greg k-h