linux-kernel - Re: nouveau crash due to missing channel (WAS: Re: [ANNOUNCE] 3.12.12-rt19)

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Message-ID: <20140307115357.GB8637@linutronix.de>
Date:	Fri, 7 Mar 2014 12:53:57 +0100
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Maarten Lankhorst <maarten.lankhorst@...onical.com>
Cc:	Fernando Lopez-Lezcano <nando@...ma.Stanford.EDU>,
	Ben Skeggs <bskeggs@...hat.com>,
	Peter Hurley <peter@...leysoftware.com>,
	linux-rt-users <linux-rt-users@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	dri-devel@...ts.freedesktop.org,
	Thomas Gleixner <tglx@...utronix.de>, rostedt@...dmis.org,
	John Kacur <jkacur@...hat.com>
Subject: Re: nouveau crash due to missing channel (WAS: Re: [ANNOUNCE]
 3.12.12-rt19)

* Maarten Lankhorst | 2014-03-07 12:36:13 [+0100]:

>>I can't find any kind of locking so my question is what ensures that chan is
>>not set to NULL between nouveau_fence_done() and
>>nouveau_fence_wait_uevent()? There are just a few opcodes in between but
>>nothing that pauses nouveau_fence_signal().
>Absolutely nothing. :-) Worse still, there's no guarantee that channel isn't freed, but hopefully that is less likely to be an issue.

Okay, so I hit the correct spot. What do we do here? Do you want the
patch I posted without the WARN_ON() or do you prefer to fix this in an
other way?

>~Maarten

Sebastian
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