Messages in this thread Patch in this message | | | Date | Wed, 4 Sep 2019 11:26:36 -0400 (EDT) | From | Mathieu Desnoyers <> | Subject | Re: [RFC PATCH 1/2] Fix: sched/membarrier: p->mm->membarrier_state racy load |
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----- On Sep 4, 2019, at 7:49 AM, Peter Zijlstra peterz@infradead.org wrote:
> On Wed, Sep 04, 2019 at 01:28:19PM +0200, Peter Zijlstra wrote: >> @@ -196,6 +198,17 @@ static int membarrier_register_global_expedited(void) >> */ >> smp_mb(); >> } else { >> + struct task_struct *g, *t; >> + >> + read_lock(&tasklist_lock); >> + do_each_thread(g, t) { >> + if (t->mm == mm) { >> + atomic_or(MEMBARRIER_STATE_GLOBAL_EXPEDITED, >> + &t->membarrier_state); >> + } >> + } while_each_thread(g, t); >> + read_unlock(&tasklist_lock); >> + >> /* >> * For multi-mm user threads, we need to ensure all >> * future scheduler executions will observe the new > > Arguably, because this is exposed to unpriv users and a potential > preemption latency issue, we could do it in 3 passes: > > - RCU, mark all found lacking, count > - RCU, mark all found lacking, count > - if count of last pass, tasklist_lock > > That way, it becomes much harder to trigger the bad case. > > Do we worry about that?
Allowing unprivileged processes to iterate over all processes/threads with the tasklist lock held is something I try to avoid.
Thanks,
Mathieu
-- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
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