Re: Linux 2.5.69

[David van Hoose <davidvh@cox.net>]

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.

Okay.. I kept having all of those problems. I guess the memory 
corruption could also explain the buffer overflow in the panic 
information I posted around the time of 2.5.65 then. I'll stick the beta 
kernel back on my system and play with it again. If I find anything 
else, I'll be sure to mention it. Don't want any nasty bugs like that 
hiding in 2.6.x.

Thanks!
David