Re: [SMP lock BUG?] Re: Feedback on preemptible kernel patch

Manfred Spraul (
Sun, 9 Sep 2001 01:11:05 +0200

> This is interesting. [Assumes UP Athlon - correct]
> Note that all BUGs out in highmem.h:95 (kmap_atomic)
> and that test is only on if you have enabled HIGHMEM_DEBUG
> [my analyze is done with a 2.4.10-pre2 kernel, but I checked with
> later patches and I do not think they fix it either...]
> The preemptive kernel puts more SMP stress on the kernel than
> running with multiple CPUs.
> So this might be a potential bug in the kernel proper, running with
> a SMP computer.

It seems to be a missing ctx_sw_off() in highmem.h:
kmap_atomic uses a per-cpu variable, thus ctx_sw_off() is needed in
kmap_atomic, and ctx_sw_on() in kunmap_atomic().


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