On Wed, Sep 30 2020 at 19:03, Peter Zijlstra wrote:
> On Wed, Sep 30, 2020 at 05:40:08PM +0200, Thomas Gleixner wrote:
> Also, that preempt_disable() in there doesn't actually do anything.
> Worse, preempt_disable(); for_each_cpu(); is an anti-pattern. It mixes
> static_cpu_has() and boot_cpu_has() in the same bloody condition and has
> a pointless ret variable.
I absolutely agree and I really missed it when looking at it before
merging. cpus_read_lock()/unlock() is the right thing to do if at all.
> It's shoddy code, that only works if you align the planets right. We
> really shouldn't provide interfaces that are this bad.
>
> It's correct operation is only by accident.
True :(
I understand Balbirs problem and it makes some sense to provide a
solution. We can:
1) reject set_affinity() if the task has that flush muck enabled
and user space tries to move it to a SMT enabled core
2) disable the muck if if detects that it is runs on a SMT enabled
core suddenly (hotplug says hello)
This one is nasty because there is no feedback to user space
about the wreckage.
Thanks,
tglx
