Messages in this thread | | | From | Milton Miller <> | Subject | Re: Make sure we populate the initroot filesystem late enough | Date | Mon, 26 Feb 2007 10:44:20 -0600 |
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On Feb 27, 2007, at 2:24 AM, David Woodhouse wrote: > On Sun, 2007-02-25 at 20:13 -0800, Linus Torvalds wrote: >> On Sun, 25 Feb 2007, David Woodhouse wrote: >>>> Can you try adding something like >>>> >>>> memset(start, 0xf0, end - start); >>> >>> Yeah, I did that before giving up on it for the day and going in >>> search >>> of dinner. It changes the failure mode to a BUG() in >>> cache_free_debugcheck(), at line 2876 of mm/slab.c >> >> Ok, that's just strange. > > In this case I hadn't left the 'return' in free_initrd_mem(). I was > poisoning the pages and then returning them to the pool as usual. > > If I poison the pages and _don't_ return them to the pool, it boots > fine. PageReserved is set on every page in the initrd region; total > page_count() is equal to the number of pages (which doesn't > _necessarily_ mean that page_count() for every page is equal to 1 but > it's a strong hint that that's the case). > > Looking in /dev/mem after it boots, I see that my poison is still > present throughout the whole region. > >> One obvious thing to do would be to remove all the "__initdata" >> entries in >> mm/slab.c.. > > This is biting us long before we call free_initmem(). > >> But I'd also like to see the full backtrace for the BUG_ON(), >> in case that gives any clues at all. > > I'll see if I can find a camera. > >>> It smells like the pages weren't actually reserved in the first place >>> and we were blithely allocating them. The only problem with that >>> theory >>> is that the initrd doesn't seem to be getting corrupted -- and if we >>> were handing out its pages like that then surely _something_ would >>> have >>> scribbled on it before we tried to read it. >> >> Yeah, I don't think it's necessarily initrd itself, I'd be more >> inclined >> to think that the reason you see this change with the initrd >> unpacking is >> simply that it does a lot of allocations for the initrd files, so I >> think >> it is only indirectly involved - just because it ends up being a slab >> user. > > Whatever happens, initrd as a 'slab user' is fine. The crashes happen > _later_, when someone else is using the memory which used to belong to > the initrd. In that 'BUG at slab.c:2876' I mentioned above, r3 was > within the initrd region. As I said, I'll try to find a camera.
Just a thought,
Any chance you are using one of the unusal code paths, like the bootloader moving the initrd or using a kernel-crash region?
milton
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