From mboxrd@z Thu Jan 1 00:00:00 1970 From: Juri Lelli Subject: Re: [PATCH V3 04/10] sched/core: Prevent race condition between cpuset and __sched_setscheduler() Date: Wed, 14 Feb 2018 11:49:35 +0100 Message-ID: <20180214104935.GS12979@localhost.localdomain> References: <1518553967-20656-1-git-send-email-mathieu.poirier@linaro.org> <1518553967-20656-5-git-send-email-mathieu.poirier@linaro.org> <20180214103639.GR12979@localhost.localdomain> Mime-Version: 1.0 Return-path: Content-Disposition: inline In-Reply-To: <20180214103639.GR12979-bi+AKbBUZKY6gyzm1THtWbp2dZbC/Bob@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Mathieu Poirier Cc: peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org, lizefan-hv44wF8Li93QT0dZR+AlfA@public.gmane.org, mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, rostedt-nx8X9YLhiw1AfugRpC6u6w@public.gmane.org, claudio-YOzL5CV4y4YG1A2ADO40+w@public.gmane.org, bristot-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, tommaso.cucinotta-5rdYK369eBLQB0XuIGIEkQ@public.gmane.org, luca.abeni-5rdYK369eBLQB0XuIGIEkQ@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org On 14/02/18 11:36, Juri Lelli wrote: > Hi Mathieu, > > On 13/02/18 13:32, Mathieu Poirier wrote: > > No synchronisation mechanism exist between the cpuset subsystem and calls > > to function __sched_setscheduler(). As such it is possible that new root > > domains are created on the cpuset side while a deadline acceptance test > > is carried out in __sched_setscheduler(), leading to a potential oversell > > of CPU bandwidth. > > > > By making available the cpuset_mutex to the core scheduler it is possible > > to prevent situations such as the one described above from happening. > > > > Signed-off-by: Mathieu Poirier > > --- > > [...] > > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > > index f727c3d0064c..0d8badcf1f0f 100644 > > --- a/kernel/sched/core.c > > +++ b/kernel/sched/core.c > > @@ -4176,6 +4176,13 @@ static int __sched_setscheduler(struct task_struct *p, > > } > > > > /* > > + * Make sure we don't race with the cpuset subsystem where root > > + * domains can be rebuilt or modified while operations like DL > > + * admission checks are carried out. > > + */ > > + cpuset_lock(); > > + > > + /* > > Mmm, I'm afraid we can't do this. __sched_setscheduler might be called > from interrupt contex by normalize_rt_tasks(). Maybe conditionally grabbing it if pi is true could do? I guess we don't care much about domains when sysrq.