linux-kernel - Re: [Bug] INFO: task hung in hub

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Message-ID: <2024030428-graph-harmful-1597@gregkh>
Date: Mon, 4 Mar 2024 17:36:19 +0100
From: Greg KH <gregkh@...uxfoundation.org>
To: Alan Stern <stern@...land.harvard.edu>
Cc: Sam Sun <samsun1006219@...il.com>, Tejun Heo <tj@...nel.org>,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
	"xrivendell7@...il.com" <xrivendell7@...il.com>,
	hgajjar@...adit-jv.com, quic_ugoswami@...cinc.com,
	stanley_chang@...ltek.com, heikki.krogerus@...ux.intel.com
Subject: Re: [Bug] INFO: task hung in hub_activate

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