Re: User-mode linux stack overflow: could be generic problem

From: Jeff Dike (
Date: Mon Oct 09 2000 - 01:25:54 EST said:
> __restore(): 764
> do_execve: 340
> load_elf_binary: 324
> segv: 180
> sigio_handler: 176
> load_script: 172
> ext2_get_block: 160
> set_signals: 156
> block_read_full_page: 124

There's nothing really fixable here.

> All up, there's about 660 bytes of stack which can be relatively
> easily saved by converting locals to kmalloced memory, which still
> isn't enough to solve the problem.

Yeah. I did get rid of the fd_set in sigio_handler, saving another 128 bytes.

Basically, UML is being screwed by the signal frame size.

> I haven't looked into UML's interrupt handling, but perhaps another
> approach is to try and avoid recursive interrupts/exceptions and do
> some kind of tail-recursion optimisation in the exception/signal
> handler. I don't know if this would cause problems (deadlocks?).

Probably :-)

I don't really want to fiddle with that, because that will impose constraints
that will hurt responsiveness.

> Alternatively, could you just use a bigger stack?

*ding ding ding* We have a winner.

I'm going to allocate 4 pages instead of two, and either have three of them
available for the stack or have two available for the stack and the third
unmapped to protect the task structure.


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