Re: task switching at Page Faults

From: Andi Kleen
Date: Mon Apr 19 2004 - 16:54:35 EST

Fabiano Ramos <ramos_fabiano@xxxxxxxxxxxx> writes:
> kernel", about 2.4, and the authors:
> 1)assure that there is no process switch during
> the execution of an eception handler (aka syscall).
> they emphasize it.

They're wrong. First the system call or exception can
block and then when kernel code returns to user space
it always checks if the time slice hasn't expired.

> 2) say that the execption handler may not generate
> exceptions, except for page faults.

That's also incorrect. e.g. it can generate GPFs
(e.g. when trying to load a segment register supplied
by the user and it is not correct)
and a few other exceptions in extreme cases. Usually
these exceptions are handled without sleeping though.


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