Re: Linux 2.6.25-rc2

[Torsten Kaiser]

On Feb 19, 2008 5:20 PM, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> So:
>  - it might be something else entirely
>  - it might still be the local cmpxchg, just Torsten didn't happen to
>    notice it until later.

My new hackbench-testcase also killed 2.6.24-rc2-mm1, so I really
noticed to late.

>  - it might still be the local cmpxchg, but something else changed its
>    patterns to actually make it start triggering.
>
> and in general I don't think we should revert it unless we have stronger
> indications that it really is the problem (eg somebody finds the actual
> bug, or a reporter can confirm that it goes away when the local cmpxchg
> optimization is disabled).

I tried the following three patches:

switching the barrier() for a smp_mb() in 2.6.25-rc2-mm1:
-> crashed

reverting the FASTPATH-patch in 2.6.25-rc2:
-> worked

only removed FAST_CMPXCHG_LOCAL from arch/x86/Kconfig
-> worked

So all of these tests seem to confirm, that the bug is in the new SLUB fastpath.

Torsten
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