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

[Lance Yang <lance.yang@linux.dev>]

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.