linux-kernel - Re: [bug] WARNING: at drivers/char/tty_io.c:1266 tty

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Date:	Tue, 16 Jun 2009 21:43:32 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	linux-kernel@...r.kernel.org,
	Pekka Enberg <penberg@...helsinki.fi>,
	Vegard Nossum <vegard.nossum@...il.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [bug] WARNING: at drivers/char/tty_io.c:1266
	tty_open+0x1ea/0x388()


* Alan Cox <alan@...rguk.ukuu.org.uk> wrote:

> > I'm wondering, how long have these patches been in linux-next? 
> > Has no-one reported an easy (or easier) reproducer than a plain 
> > bootup (which really doesnt hit the tty code intentionally 
> > hard)?
> 
> Quite a while - and the open side stuff hasn't changed in the post 
> 2.6.30 patches at all. Your box seems to show stuff up that most 
> users just don't hit.

Another box has triggered that too btw. But with your two fixes:

 69e8fd4: tty: fix sanity check
 9f7a9ce: ldisc: Make sure the ldisc isn't active when we close it

i havent seen any new tty warnings today. (testing is a bit spotty 
due to other bugs though - this is typical of the merge window.)

Also, the only warning that remained after your fix was the new 
warning you added to catch an old bug - that's not a regression 
really.

> > You should probably also write testcases and stress-tests if you 
> > modify code in this area.
> 
> I did - they hang the tty layers in 2.6.30 and earlier in about 60 
> seconds, it then corrupts the module counts and dies shortly 
> after. I've not published them because they can obviously be 
> seriously misused.

Too bad - i could have ran them in the test mix.

> I don't have the luxury of building on solid foundations trying to 
> sort the tty layer out - its been broken since 2.1.x when the 
> lock_kernel logic stopped applying to IRQ handlers.

No complaints from me at all! You are doing fantastic cleanups and 
fixes in the TTY code.

	Ingo
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