Breakage in "track dev_mapping in more robust and flexible way"

Ilija Hadzic ilijahadzic at
Thu Oct 25 10:12:04 PDT 2012

On Thu, Oct 25, 2012 at 11:10 AM, Thomas Hellström
<thellstrom at> wrote:
> On 10/25/12 4:41 PM, Jerome Glisse wrote:
>> On Thu, Oct 25, 2012 at 04:02:25PM +0200, Thomas Hellstrom wrote:
>>> Hi,
>>> This commit
>>>  From 949c4a34afacfe800fc442afac117aba15284962 Mon Sep 17 00:00:00 2001
>>> From: Ilija Hadzic <ihadzic at>
>>> Date: Tue, 15 May 2012 16:40:10 -0400
>>> Subject: [PATCH] drm: track dev_mapping in more robust and flexible way
>>> Setting dev_mapping (pointer to the address_space structure
>>> used for memory mappings) to the address_space of the first
>>> opener's inode and then failing if other openers come in
>>> through a different inode has a few restrictions that are
>>> eliminated by this patch.
>>> If we already have valid dev_mapping and we spot an opener
>>> with different i_node, we force its i_mapping pointer to the
>>> already established address_space structure (first opener's
>>> inode). This will make all mappings from drm device hang off
>>> the same address_space object.
>>> ...
>>> Breaks drivers using TTM, since when the X server calls into the
>>> driver open, drm's dev_mapping has not
>>> yet been setup. The setup needs to be moved before the driver's open
>>> hook is called.
>>> Typically, if a TTM-aware driver is provoked by the Xorg server to
>>> move a buffer from system to VRAM or AGP,
>>> before any other drm client is started, The user-space page table
>>> entries are not killed before the move, and left pointing
>>> into freed pages, causing system crashes and / or user-space access
>>> to arbitrary memory.
>> Doesn't handle move invalidate the drm file mapping before scheduling
>> the move ?
> Yes, but to do that it needs a correct value of bdev::dev_mapping, which is
> now incorrectly set on the
> *second* open instead of the first open.

So you are implying that in the first open the assignment of dev->dev_mapping is
somehow skipped (which could happen if drm_setup returns an error) or that the
driver on which you are having problems with (nouveau I presume) needs
in the firstopen hook ?

It's been a while since I did it, but if my memory serves me well I
thought I explicitly
verified that dev_mapping was correctly set in the first open (though
GPUs I use are
primarily AMD).

-- Ilija

> /Thomas
>> Cheers,
>> Jerome
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