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Date: Mon, 4 Mar 2024 13:30:35 -0500
From: Alan Stern <stern@rowland.harvard.edu>
To: Greg KH <gregkh@linuxfoundation.org>
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
Message-ID: <416a8311-c725-419a-8b22-74c80207347f@rowland.harvard.edu>
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On Mon, Mar 04, 2024 at 05:36:19PM +0100, Greg KH wrote:
> 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.

Are you thinking of the sysfs_break_active_protection() and 
sysfs_unbreak_active_protection() functions?  They seem to be the 
appropriate ones to use here.

Alan Stern