Messages in this thread Patch in this message | | | Date | Wed, 06 Apr 2005 19:44:54 +0400 | From | Stas Sergeev <> | Subject | Re: crash in entry.S restore_all, 2.6.12-rc2, x86, PAGEALLOC |
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Hi,
Linus Torvalds wrote: > Yes. But how do you have _such_ an empty stack when the interrupt comes > in? See what I mean? Yes, I hope so.
> IOW, that requires that the kernel stack would have > only two words on it when the interrupt happens. How? Well, you can simply do something like this:
--- entry.S.old1 2005-04-05 22:54:43.000000000 +0400 +++ entry.S 2005-04-06 19:35:14.000000000 +0400 @@ -179,9 +179,9 @@ ENTRY(sysenter_entry) movl TSS_sysenter_esp0(%esp),%esp sysenter_past_esp: - sti pushl $(__USER_DS) pushl %ebp + sti pushfl pushl $(__USER_CS) pushl $SYSENTER_RETURN And this will "elimenate" the problem (modulo NMI and there could be other places too, but for me it elimenates it completely). So I don't think this is something strange.
> So I definitely think the "bug" is in your optimization, Yes, and I think the patch I posted, can just work, or are there the problems with the taken forward jump on a fast path?
> I just think it > should be a valid optimization But it is totally bogus, why not should it crash? It is probably even very good that it does:)
> and we should just make sure our kernel > stack is never _so_ empty that "struct pt_regs" is not safe to > dereference. I guess you'll just need to adjust the tss.esp0 then, but do you really want this? Accesing the registers that are simply not there, doesn't sound too good I think. Or am I still missing your point?
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