Re: Linux 2.5.69

[Steven Cole]

On Mon, 2003-05-05 at 09:56, Linus Torvalds wrote:
> [ Linux-kernel added to the cc, since I got several queries about what the 
>   crashes were.. ]
> 
> On Mon, 5 May 2003, David van Hoose wrote:
> > 
> > Can I get some details regarding the AGP problem? I had some really bad 
> > random crashes, panics, and hardlocks up through 2.5.68, and I'm 
> > wondering if this is the same issue. I first noticed them around 2.5.63. 
> 
> They actually started in 2.5.60 if it's the same bug.
> 
> And yes, you'd get random crashes, panics, lockups and even reboots. The 
> problem was that the pmd/pgd's were put in the slab cache in between 
> 2.5.59 and 2.5.60, and that was simply wrong because the AGP code changes 
> the cacheability of the kernel pages when it maps stuff into the AGP 
> aperture. That in turn will change the page tables but it won't update the 
> cached entries in the pmd slab caches. 
> 
> So what happens is that once you exit X, and the page tables are put back
> together without the cacheability changes, and you start a new program,
> that program may get a page table with partly bogus kernel page table
> entries.
> 
> That, in turn, when it happens will cause _major_ memory corruption, and
> your machine is toast, often in very interesting ways because the internal
> kernel data structures got corrupted. It can also cause random SIGSEGV's
> etc.
> 
> But it only happens with AGP, and a lot of people either don't use it or 
> run only one X session.
> 
> 			Linus

This fixes a problem I reported here:
http://marc.theaimsgroup.com/?l=linux-kernel&m=104990441203933&w=2

Thanks,
Steven