Jan Kiszka wrote:
> Jan Kiszka wrote:
>> It's still unclear what goes on precisely, we are still digging, but the
>> test system that can produce this is highly contended.
> 
> Short update: Further instrumentation revealed that cr3 differs from
> active_mm->pgd while we are looping over that fault, ie. the kernel
> tries to fixup the wrong mm. And that means we have some open race
> window between updating cr3 and active_mm somewhere (isn't switch_mm run
> in a preemptible manner now?).

Maybe the rsp is wrong and leads you to the wrong active_mm ?

> 
> As a first shot I disabled CONFIG_IPIPE_DELAYED_ATOMICSW, and we are now
> checking if it makes a difference. Digging deeper into the code in the
> meanwhile...

As you have found out in the mean time, we do not use unlocked context
switches on x86.

-- 
                                          Gilles


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