linux-kernel - RE: System reboot hangs due to race against devices_kset->list triggered by SCSI FC workqueue

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Date:	Wed, 3 Mar 2010 15:25:47 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Hugh Daschbach <hdasch@...adcom.com>
cc:	Greg KH <gregkh@...e.de>, Kay Sievers <kay.sievers@...y.org>,
	Jan Blunck <jblunck@...e.de>,
	David Vrabel <david.vrabel@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	james Bottomley <James.Bottomley@...e.de>,
	James Smart <james.smart@...lex.com>
Subject: RE: System reboot hangs due to race against devices_kset->list
 triggered by SCSI FC workqueue

On Wed, 3 Mar 2010, Hugh Daschbach wrote:

> > Can't we just protect the list?  What is wanting to write to the list
> > while shutdown is happening?
> 
> Indeed, Alan suggested holding the kset spinlock while iterating the
> list.  Unfortunately, the device shutdown routines may sleep.  At least
> the SCSI sd_shutdown routine issues I/O to the device as part of
> flushing device caches.  I would guess other subsystems sleep as well.

What I meant was that you should hold the spinlock while finding and 
unlinking the last device on the list.  Clearly you shouldn't hold it 
while calling the device shutdown routine.

> I'll try klist.  That looks like a good mediator between traversal and
> removal.

Yes, it removes a lot of difficulties.

Alan Stern

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