Re: atomic copy_from_user?
From: Rob Love
Date: Mon Dec 22 2003 - 17:16:53 EST
On Mon, 2003-12-22 at 16:59, Joe Korty wrote:
> I do not see why a non-preempt kernel would care at all about
> the value of preempt_count. (kmap_atomic is obviously setting it,
> where is the place in a non-preempt kernel where the set value
> is being acted upon?).
Last I checked, the architecture-specific page fault handlers. They do
something like:
if (in_atomic())
goto do_not_service_fault;
This let us implement the atomic copy_*_user() functions.
kmap_atomic() needs to mark the system atomic, so the in_atomic() will
fail.
This was done around ~2.5.30 by akpm.
Rob Love
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