| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <aYH9Ds0yy6cRxuZI@gpd4>
Date: Tue, 3 Feb 2026 14:50:06 +0100
From: Andrea Righi <arighi@...dia.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Steven Rostedt <rostedt@...dmis.org>,
Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
Valentin Schneider <vschneid@...hat.com>, Tejun Heo <tj@...nel.org>,
Joel Fernandes <joelagnelf@...dia.com>,
David Vernet <void@...ifault.com>,
Changwoo Min <changwoo@...lia.com>,
Daniel Hodges <hodgesd@...a.com>,
Christian Loehle <christian.loehle@....com>,
Emil Tsalapatis <emil@...alapatis.com>, sched-ext@...ts.linux.dev,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/7] sched/debug: Stop and start server based on if it
was active
On Tue, Feb 03, 2026 at 11:34:07AM +0100, Peter Zijlstra wrote:
> On Mon, Feb 02, 2026 at 11:37:31PM +0100, Andrea Righi wrote:
>
> > Or:
> >
> > pr_info("%s server %sabled in CPU %d%s\n",
> > server == &rq->fair_server ? "Fair" : "Ext",
> > runtime ? "en" : "dis",
> > cpu_of(rq),
> > runtime ? "" : ", system may crash due to starvation");
>
> Yeah, I noticed it was a bit wonkey. I made it thus.
>
> > > + }
> > > +
> > > *ppos += cnt;
> > > return cnt;
> > > }
> >
> > I like that, it should fix the issue.
>
> There is one more issue when dl_server_apply_params() fails, in that
> case we should test old_runtime to determine if we should (re)start the
> dl_server.
>
> I've ended up with this.
LGTM, I also re-ran all my stress tests with this applied, everything is
working great and the runtime=0 issue is fixed.
Tested-by: Andrea Righi <arighi@...dia.com>
Thanks!
-Andrea
> Subject: sched/debug: Fix dl_server (re)start conditions
> From: Peter Zijlstra <peterz@...radead.org>
> Date: Tue Feb 3 11:05:12 CET 2026
>
> There are two problems with sched_server_write_common() that can cause the
> dl_server to malfunction upon attempting to change the parameters:
>
> 1) when, after having disabled the dl_server by setting runtime=0, it is
> enabled again while tasks are already enqueued. In this case is_active would
> still be 0 and dl_server_start() would not be called.
>
> 2) when dl_server_apply_params() would fail, runtime is not applied and does
> not reflect the new state.
>
> Instead have dl_server_start() check its actual dl_runtime, and have
> sched_server_write_common() unconditionally (re)start the dl_server. It will
> automatically stop if there isn't anything to do, so spurious activation is
> harmless -- while failing to start it is a problem.
>
> While there, move the printk out of the locked region and make it symmetric,
> also printing on enable.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
> kernel/sched/deadline.c | 5 ++---
> kernel/sched/debug.c | 32 ++++++++++++++------------------
> 2 files changed, 16 insertions(+), 21 deletions(-)
>
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -1784,7 +1784,7 @@ void dl_server_start(struct sched_dl_ent
> {
> struct rq *rq = dl_se->rq;
>
> - if (!dl_server(dl_se) || dl_se->dl_server_active)
> + if (!dl_server(dl_se) || dl_se->dl_server_active || !dl_se->dl_runtime)
> return;
>
> /*
> @@ -1882,7 +1882,6 @@ int dl_server_apply_params(struct sched_
> int cpu = cpu_of(rq);
> struct dl_bw *dl_b;
> unsigned long cap;
> - int retval = 0;
> int cpus;
>
> dl_b = dl_bw_of(cpu);
> @@ -1914,7 +1913,7 @@ int dl_server_apply_params(struct sched_
> dl_se->dl_bw = to_ratio(dl_se->dl_period, dl_se->dl_runtime);
> dl_se->dl_density = to_ratio(dl_se->dl_deadline, dl_se->dl_runtime);
>
> - return retval;
> + return 0;
> }
>
> /*
> --- a/kernel/sched/debug.c
> +++ b/kernel/sched/debug.c
> @@ -338,9 +338,9 @@ static ssize_t sched_server_write_common
> void *server)
> {
> long cpu = (long) ((struct seq_file *) filp->private_data)->private;
> - struct rq *rq = cpu_rq(cpu);
> struct sched_dl_entity *dl_se = (struct sched_dl_entity *)server;
> - u64 runtime, period;
> + u64 old_runtime, runtime, period;
> + struct rq *rq = cpu_rq(cpu);
> int retval = 0;
> size_t err;
> u64 value;
> @@ -350,9 +350,7 @@ static ssize_t sched_server_write_common
> return err;
>
> scoped_guard (rq_lock_irqsave, rq) {
> - bool is_active;
> -
> - runtime = dl_se->dl_runtime;
> + old_runtime = runtime = dl_se->dl_runtime;
> period = dl_se->dl_period;
>
> switch (param) {
> @@ -374,25 +372,23 @@ static ssize_t sched_server_write_common
> return -EINVAL;
> }
>
> - is_active = dl_server_active(dl_se);
> - if (is_active) {
> - update_rq_clock(rq);
> - dl_server_stop(dl_se);
> - }
> -
> + update_rq_clock(rq);
> + dl_server_stop(dl_se);
> retval = dl_server_apply_params(dl_se, runtime, period, 0);
> -
> - if (!runtime)
> - printk_deferred("%s server disabled in CPU %d, system may crash due to starvation.\n",
> - server == &rq->fair_server ? "Fair" : "Ext", cpu_of(rq));
> -
> - if (is_active && runtime)
> - dl_server_start(dl_se);
> + dl_server_start(dl_se);
>
> if (retval < 0)
> return retval;
> }
>
> + if (!!old_runtime ^ !!runtime) {
> + pr_info("%s server %sabled on CPU %d%s.\n",
> + server == &rq->fair_server ? "Fair" : "Ext",
> + runtime ? "en" : "dis",
> + cpu_of(rq),
> + runtime ? "" : ", system may malfunction due to starvation");
> + }
> +
> *ppos += cnt;
> return cnt;
> }
Powered by blists - more mailing lists