lkml.org 
[lkml]   [2020]   [Nov]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] sched: Fix data-race in wakeup
On Tue, Nov 17, 2020 at 03:37:24PM +0000, Valentin Schneider wrote:

> >> + /*
> >> + * This field must not be in the scheduler word above due to wakelist
> >> + * queueing no longer being serialized by p->on_cpu. However:
> >> + *
> >> + * p->XXX = X; ttwu()
> >> + * schedule() if (p->on_rq && ..) // false
> >> + * smp_mb__after_spinlock(); if (smp_load_acquire(&p->on_cpu) && //true
> >> + * deactivate_task() ttwu_queue_wakelist())
> >> + * p->on_rq = 0; p->sched_remote_wakeup = Y;
> >> + *
> >> + * guarantees all stores of 'current' are visible before
> >> + * ->sched_remote_wakeup gets used, so it can be in this word.
> >> + */
> >
> > Isn't the control dep between that ttwu() p->on_rq read and
> > p->sched_remote_wakeup write "sufficient"?
>
> smp_acquire__after_ctrl_dep() that is, since we need
> ->on_rq load => 'current' bits load + store

I don't think we need that extra barrier; after all, there will be a
complete schedule() between waking the task and it actually becoming
current.

\
 
 \ /
  Last update: 2020-11-17 17:17    [W:0.095 / U:0.312 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site