Messages in this thread | | | Date | Tue, 5 Apr 2005 22:44:36 +0200 | From | Ingo Molnar <> | Subject | Re: crash in entry.S restore_all, 2.6.12-rc2, x86, PAGEALLOC |
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* Linus Torvalds <torvalds@osdl.org> wrote:
> > > So I'd actually prefer to get that mystery explained.. > > IIRC if the interrupt doesn't do the CPL > > switch, the interrupt gate doesn't save > > the stack, and so there may not be the > > full "struct pt_regs" when the kernel > > thread is interrupted. > > Yes. But how do you have _such_ an empty stack when the interrupt > comes in? See what I mean? IOW, that requires that the kernel stack > would have only two words on it when the interrupt happens. How? > > It may be a 4kB stack issue or something. Does this happen only with > CONFIG_4KSTACKS, and just after a stack switch to an irq stack, for > example?
i didnt have 4K stacks set. In all crashes, esp had the same pattern:
esi: 009b63f9 edi: 00000001 ebp: f543a000 esp: f543bfc8
i.e. esp & 0xfff was 0xfc8 - while i think it should normally be 0xfc4 (page boundary minus size of pt_regs == 0 - 0x3c == 0xfc4). So somewhere we lost 4 bytes of esp? An extra popl, or an addl $4, %esp? But why dont we crash in that case - it ought to shift all the pt_regs structure by a word, making it a completely senseless return frame. Any task in such a situation ought to at least segfault. So if this is during thread startup, i dont know how it survives the first execution.
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