linux-kernel - Re: proper tty-ldisc refcounting (was Re: WARNING at: drivers/char/tty

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Date:	Tue, 4 Aug 2009 07:53:53 -0700
From:	Greg KH <greg@...ah.com>
To:	Sergey Senozhatsky <sergey.senozhatsky@...l.by>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: proper tty-ldisc refcounting (was Re: WARNING at:
 drivers/char/tty_ldisc.c)

On Tue, Aug 04, 2009 at 12:12:37PM +0300, Sergey Senozhatsky wrote:
> On (08/04/09 00:23), Greg KH wrote:
> > On Mon, Aug 03, 2009 at 11:19:53PM -0700, Linus Torvalds wrote:
> > > 
> > > 
> > > On Mon, 3 Aug 2009, Greg KH wrote:
> > > > 
> > > > Oh wait, the original problem, single user mode.  Hm, we need all of
> > > > these to fix that problem?  Or just the first one?
> > > 
> > > Patches 1-3 should fix that one. 4-5 are just cleanups with no semantic 
> > > changes.
> > 
> > Ok, but due to the lateness of the release cycle, is it worth it to add
> > those 3 right now?  Or do we just take the BUG_ON() out as it's pretty
> > harmless while shutting down in single user mode?
> > 
> > What do you think?
> > 
> 
> I don't think that take the BUG_ON out is the best we can do. 
> 
> If I understand correctly, this one (tty_ldisc.c:209):
> static void tty_ldisc_put(struct tty_ldisc *ld)
> {
> 	[...]
> 	spin_unlock_irqrestore(&tty_ldisc_lock, flags);
> -	WARN_ON(ld->refcount);
> 	kfree(ld);
> }
> 
> It's better to leave everything as is in that case and wait 32 (to my mind).

Sorry, you are correct, it was a WARN_ON call that caused the warning.

One other option is to put these changes into .32, and add them back to
the .31 -stable tree once it goes into Linus's tree and no one has any
reported problems.

thanks,

greg k-h
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