Bug 30647 - XServer segfaults when EXANoUploadToScreen is set.
Summary: XServer segfaults when EXANoUploadToScreen is set.
Status: RESOLVED WONTFIX
Alias: None
Product: xorg
Classification: Unclassified
Component: Driver/Radeon (show other bugs)
Version: git
Hardware: Other All
: medium normal
Assignee: xf86-video-ati maintainers
QA Contact: Xorg Project Team
URL:
Whiteboard:
Keywords:
: 30897 (view as bug list)
Depends on:
Blocks:
 
Reported: 2010-10-06 03:19 UTC by Rafael Monica
Modified: 2010-10-15 13:20 UTC (History)
1 user (show)

See Also:
i915 platform:
i915 features:


Attachments
backtrace (2.57 KB, text/plain)
2010-10-06 03:19 UTC, Rafael Monica
no flags Details

Description Rafael Monica 2010-10-06 03:19:42 UTC
Created attachment 39216 [details]
backtrace

Setting the EXANoUploadToScreen option in xorg.conf makes the xserver segfault. 

git bisect says:

f8fb9312d791af1f77020e8c2d35bb30841ed9aa is the first bad commit
commit f8fb9312d791af1f77020e8c2d35bb30841ed9aa
Author: Karl Tomlinson <karlt+@karlt.net>
Date:   Sun Aug 22 22:46:33 2010 +1200

    RADEONPrepareAccess_CS: fallback to DFS when pixmap is in VRAM

    This avoids costly CPU VRAM reads and lets EXA manage a system memory cache
    of the portions of pixmaps needed for unaccelerated operations.

    https://bugs.freedesktop.org/show_bug.cgi?id=27139
Comment 1 Michel Dänzer 2010-10-06 07:02:02 UTC
I'm inclined to resolve this as WONTFIX. This is a useful optimization, and the driver has required the UploadToScreen hook on big endian machines for as long as KMS has worked there.

Why are you trying to use Option "EXANoUploadToScreen"?
Comment 2 Rafael Monica 2010-10-06 10:49:01 UTC
I agree it's a useful optimization and WONTFIX is fine with me, although I think it would be cleaner to disable EXANoUploadToScreen option, or at least mention it in exa(4) that this option causes segfault with radeon driver.

I was trying this option because of bug 30188, which gives me EVERGREENUploadToScreen in the backtrace, and was hoping EXANoUploadToScreen option would fix it, unfortunately it doesn't.
Comment 3 Michel Dänzer 2010-10-07 02:42:31 UTC
(In reply to comment #2)
> I agree it's a useful optimization and WONTFIX is fine with me, although I
> think it would be cleaner to disable EXANoUploadToScreen option,

Not possible, it's an option of the "exa" module, which doesn't know that the driver really needs the UploadToScreen hook.

> or at least mention it in exa(4) that this option causes segfault with radeon
> driver.

If anything it should rather be documented with the driver.


> I was trying this option because of bug 30188, which gives me
> EVERGREENUploadToScreen in the backtrace, and was hoping EXANoUploadToScreen
> option would fix it, unfortunately it doesn't.

Trying to work around that problem really requires the UploadTo/DownloadFromScreen hooks. The issue is that there is still sometimes direct CPU access to VRAM.
Comment 4 Alex Deucher 2010-10-15 13:20:37 UTC
*** Bug 30897 has been marked as a duplicate of this bug. ***


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