linux-kernel - Re: [RFC PATCH] drm/nouveau: fix nested locking in mmap handler

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Message-ID: <5241C60B.9070706@vmware.com>
Date:	Tue, 24 Sep 2013 19:04:11 +0200
From:	Thomas Hellstrom <thellstrom@...are.com>
To:	Maarten Lankhorst <maarten.lankhorst@...onical.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Dave Airlie <airlied@...ux.ie>,
	intel-gfx <intel-gfx@...ts.freedesktop.org>,
	dri-devel <dri-devel@...ts.freedesktop.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ben Skeggs <bskeggs@...hat.com>,
	Alex Deucher <alexander.deucher@....com>
Subject: Re: [RFC PATCH] drm/nouveau: fix nested locking in mmap handler

On 09/24/2013 01:32 PM, Maarten Lankhorst wrote:
> Op 24-09-13 12:33, Thomas Hellstrom schreef:
>> On 09/24/2013 12:11 PM, Maarten Lankhorst wrote:
>>>
>>> It seems userspace only updates offset and domain in nouveau. If it fails to update
>>> it would result in the same affect as when the buffer gets moved around by TTM.
>>> But hey maybe I'll have some fun, I'll lie to userspace, hardcode userspace offset
>>> to 0x40000000, always force domain to be different and see what breaks.
>>>
>>> My guess is absolutely nothing, except it might expose some bugs where we forgot annotation..
>> I think that would certainly break if your return an -ERESTARTSYS after applying relocations but
>> before submitting the command stream to hardware....
> The relocations are updated before submitting the command stream, but it's copied back to userspace
> after submitting the command stream. I'm not sure what -ERESTARTSYS would change, the syscall
> is not in an interruptible state.
Hmm, I was assuming without looking at the code that there was an 
interruptible wait for pipe/ring space after
relocation application.

/Thomas
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