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

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Date: Tue, 5 Mar 2024 12:03:03 +0000
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 01:30:35PM -0500, Alan Stern wrote:
> 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.

Yes, that sounds correct.