linux-kernel - Re: [PATCH] tty: add lockdep annotations

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Message-ID: <1338584389.2760.1653.camel@edumazet-glaptop>
Date:	Fri, 01 Jun 2012 22:59:49 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Alan Cox <alan@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jens Axboe <jaxboe@...ionio.com>
Subject: Re: [PATCH] tty: add lockdep annotations

On Fri, 2012-06-01 at 21:56 +0100, Alan Cox wrote:
> > Yes, tty->driver deref is ok (tty points to valid memory), but crash is
> > on tty->driver->ops (driver points to freed/illegal memory)
> > 
> > using slub_debug=FZPU, I can indeed see RDI=6b6b6b6b6b6b6b6b
> 
> driver and driver->ops is basically const and it's not what you'd expect
> from a tty refcount bug. The driver side puts shouldn't have changed but
> I'll take a look over that patch and the error paths closely again just
> in case.

right

The code looks like :
...
	call mcount
	mov  %rdi,%rbx
	mov  0x10(%rdi),%rdi   tty->driver
<>	mov  0xf8(%rdi),%rax   CRASH

So tty was freed an tty->driver contains 6b6b6b6b6b6b6b6b



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