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XSHM/shared-pixmap fix Was: Linux Shared Memory Issue

To: ralf@oss.sgi.com
Subject: XSHM/shared-pixmap fix Was: Linux Shared Memory Issue
From: Florian Lohoff <flo@rfc822.org>
Date: Sat, 27 Apr 2002 23:45:05 +0200
Cc: linux-mips@oss.sgi.com, agx@sigxcpu.org
In-reply-to: <3CC72BA3.90600@mvista.com>
Organization: rfc822 - pure communication
References: <NDBBKEAAOJECIDBJKLIHOEDDCDAA.turcotte@broadcom.com> <3CC72BA3.90600@mvista.com>
Sender: owner-linux-mips@oss.sgi.com
User-agent: Mutt/1.3.28i
Hi Ralf, *,

On Wed, Apr 24, 2002 at 03:03:15PM -0700, Jun Sun wrote:
> Looks like the infamous cache aliasing problem.  Steve Longerbeam had a 
> patch which may help.  Please try it and let me know the results.

> Maurice Turcotte wrote:
> >I am having a problem with Linux Kernel 2.4.5 on a mips.
> >
> >I have two processes using share memory for IPC. This same
> >code works fine with Kernel 2.4.7 on a x86. The problem is 
> >that the second process reads old data out of the shared
> >memory.
> >
> >The executive summary->
> >
> >Process #1 writes "A" to shared memory at 0x2aac7210
> >Process #2 reads 0 from shared memory at address 0x2aaca210
> >Process #1 writes "B" to shared memory at 0x2aac7210
> >Process #2 read "A" from shared memory at address 0x2aaca210
> >Process #1 writes "C" to shared memory at 0x2aac7210
> >Process #2 read "B" from shared memory at address 0x2aaca210
> >

I today tried the patch in conjunction with XFree86 and XSHM on
an Indy R5000/150. Usually all gtk shared-pixmaps get destroyed
and written lines in it. With this patch all these garbage disappears.
As long as there a no serious issues against this patch i would
vote for inclused. It applies against todays cvs with only little
offsets and gave me no problems. It definitly solves some serious
issues with shm.

Flo
-- 
Florian Lohoff                  flo@rfc822.org             +49-5201-669912
Nine nineth on september the 9th              Welcome to the new billenium

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