Re: uprobe splat in PREEMP_RT

Sebastian Sewior
2025-04-02T12:16:27Z

On 2025-04-02 14:12:28 [+0200], Oleg Nesterov wrote:
> On 04/02, Sebastian Sewior wrote:
> >
> > On 2025-04-02 13:31:43 [+0200], Oleg Nesterov wrote:
> > >
> > > IOW.
> > >
> > > I understand that seqcount_t is not RT-friendly, but why exactly do
> > > you think the patch above can make the things worse?
> >
> > We wouldn't notice such a case.
>
> Sebastian, could you spell please?
>
> What case we wouldn't notice?

I'm sorry. It wouldn't notice that preemption isn't disabled and yell.

> With this patch write_seqcount_begin(seqcount_t) will notice that
> seqprop_preemptible() is true and do preempt_disable() itself.

Yes, but that we don't want. This would disable preemption for the whole
section and not allow anything on PREEMPT_RT what would be possible
otherwise. Like acquire a spinlock_t or so.

Yes, none of this would affect hprobe_expire().

> Oleg.

Sebastian