linux-kernel - Re: [RFC PATCH] drm/radeon: fixup locking inversion between mmap

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Message-ID: <52541A95.4040107@canonical.com>
Date:	Tue, 08 Oct 2013 16:45:41 +0200
From:	Maarten Lankhorst <maarten.lankhorst@...onical.com>
To:	Jerome Glisse <j.glisse@...il.com>
CC:	Thomas Hellstrom <thellstrom@...are.com>,
	Alex Deucher <alexander.deucher@....com>,
	Peter Zijlstra <peterz@...radead.org>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	intel-gfx <intel-gfx@...ts.freedesktop.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	dri-devel <dri-devel@...ts.freedesktop.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [RFC PATCH] drm/radeon: fixup locking inversion between mmap_sem
 and reservations

op 08-10-13 16:33, Jerome Glisse schreef:
> On Tue, Oct 08, 2013 at 04:14:40PM +0200, Maarten Lankhorst wrote:
>> Allocate and copy all kernel memory before doing reservations. This prevents a locking
>> inversion between mmap_sem and reservation_class, and allows us to drop the trylocking
>> in ttm_bo_vm_fault without upsetting lockdep.
>>
>> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@...onical.com>
> I would say NAK. Current code only allocate temporary page in AGP case.
> So AGP case is userspace -> temp page -> cs checker -> radeon ib.
>
> Non AGP is directly memcpy to radeon IB.
>
> Your patch allocate memory memcpy userspace to it and it will then be
> memcpy to IB. Which means you introduce an extra memcpy in the process
> not something we want.
>
Can we move up the call to radeon_ib_get then to be done before calling radeon_cs_parser_relocs?

~Maarten
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