Re: [PATCH RFC] mm/kmemleak: avoid soft lockup when scanning task stacks

[Lance Yang]

On 2026/6/12 18:39, Breno Leitao wrote:
> On Fri, Jun 12, 2026 at 05:57:12PM +0800, Lance Yang wrote:
>
> > > If we go this route, the aborted round has to suppress reporting, reusing
> > > kmemleak's existing "scan was interrupted -> don't report" path:
> > >
> > >         if (need_resched() && !kmemleak_stack_scan_break(g, p)) {
> > >                 aborted = true;
> > >                 goto unlock;
> > >         }
> >
> > I'd expect the normal case to just drop RCU, cond_resched(), take RCU
> > again, see both cursors still alive, and keep walking :)
> >
> > >         ...
> > >         if (scan_should_stop() || aborted)
> > >                 return;
> >
> > And yeah, you're right. If we do lost a cursor, bailing out and
> > skipping reporting fot that incomplete root scan should be the
> > right thing, I guess :D
>
> Thanks! Under what circumstances would the cursor actually be lost?

It should be race, but possible, that we happen to stop on g/p,
drop RCU, and one of them is gone by the time we come back.