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Fri, 27 Jun 2025 01:05:25 -0700 (PDT) X-Google-Smtp-Source: AGHT+IFaMJrRYRhoRLux+vk+OsIiQlv9TTSam8bVtWhu6PiNh+mKCLTZbj8uRsmMNhufOC+vLn4+3w== X-Received: by 2002:adf:b604:0:b0:3a5:2670:e220 with SMTP id ffacd0b85a97d-3a8fdeff974mr1872359f8f.32.1751011525109; Fri, 27 Jun 2025 01:05:25 -0700 (PDT) Received: from jlelli-thinkpadt14gen4.remote.csb ([176.206.11.85]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45380d628c6sm42196755e9.3.2025.06.27.01.05.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 27 Jun 2025 01:05:23 -0700 (PDT) Date: Fri, 27 Jun 2025 10:05:21 +0200 From: Juri Lelli To: Yicong Yang Cc: mingo@redhat.com, peterz@infradead.org, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, linux-kernel@vger.kernel.org, linuxarm@huawei.com, prime.zeng@hisilicon.com, yangyicong@hisilicon.com Subject: Re: [PATCH] sched/deadline: Don't count nr_running twice for dl_server proxy tasks Message-ID: References: <20250627035420.37712-1-yangyicong@huawei.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250627035420.37712-1-yangyicong@huawei.com> Hello, On 27/06/25 11:54, Yicong Yang wrote: > From: Yicong Yang > > On CPU offline the kernel stalled with below call trace: > > INFO: task kworker/0:1:11 blocked for more than 120 seconds. > Tainted: G O 6.15.0-rc4+ #1 > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > task:kworker/0:1 state:D stack:0 pid:11 tgid:11 ppid:2 task_flags:0x4208060 flags:0x00000008 > Workqueue: events vmstat_shepherd > Call trace: > __switch_to+0x118/0x188 (T) > __schedule+0x31c/0x1300 > schedule+0x3c/0x120 > percpu_rwsem_wait+0x12c/0x1b0 > __percpu_down_read+0x78/0x188 > cpus_read_lock+0xc4/0xe8 > vmstat_shepherd+0x30/0x138 > process_one_work+0x154/0x3c8 > worker_thread+0x2e8/0x400 > kthread+0x154/0x230 > ret_from_fork+0x10/0x20 > INFO: task kworker/1:1:116 blocked for more than 120 seconds. > Tainted: G O 6.15.0-rc4+ #1 > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > task:kworker/1:1 state:D stack:0 pid:116 tgid:116 ppid:2 task_flags:0x4208060 flags:0x00000008 > Workqueue: events work_for_cpu_fn > Call trace: > __switch_to+0x118/0x188 (T) > __schedule+0x31c/0x1300 > schedule+0x3c/0x120 > schedule_timeout+0x10c/0x120 > __wait_for_common+0xc4/0x1b8 > wait_for_completion+0x28/0x40 > cpuhp_kick_ap_work+0x114/0x3c8 > _cpu_down+0x130/0x4b8 > __cpu_down_maps_locked+0x20/0x38 > work_for_cpu_fn+0x24/0x40 > process_one_work+0x154/0x3c8 > worker_thread+0x2e8/0x400 > kthread+0x154/0x230 > ret_from_fork+0x10/0x20 > > cpuhp hold the cpu hotplug lock endless and stalled vmstat_shepherd. > This is because we count nr_running twice on cpuhp enqueuing and failed > the wait condition of cpuhp: > > enqueue_task_fair() // pick cpuhp from idle, rq->nr_running = 0 > dl_server_start() > [...] > add_nr_running() // rq->nr_running = 1 > add_nr_running() // rq->nr_running = 2 > [switch to cpuhp, waiting on balance_hotplug_wait()] > rcuwait_wait_event(rq->nr_running == 1 && ...) // failed, rq->nr_running=2 > schedule() // wait again > > This doesn't make sense to count one single task twice on > rq->nr_running. So fix this. > > Signed-off-by: Yicong Yang > --- > kernel/sched/deadline.c | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) > > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c > index ad45a8fea245..59fb178762ee 100644 > --- a/kernel/sched/deadline.c > +++ b/kernel/sched/deadline.c > @@ -1894,7 +1894,9 @@ void inc_dl_tasks(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq) > u64 deadline = dl_se->deadline; > > dl_rq->dl_nr_running++; > - add_nr_running(rq_of_dl_rq(dl_rq), 1); > + > + if (!dl_server(dl_se)) > + add_nr_running(rq_of_dl_rq(dl_rq), 1); > > inc_dl_deadline(dl_rq, deadline); > } > @@ -1904,7 +1906,9 @@ void dec_dl_tasks(struct sched_dl_entity *dl_se, struct dl_rq *dl_rq) > { > WARN_ON(!dl_rq->dl_nr_running); > dl_rq->dl_nr_running--; > - sub_nr_running(rq_of_dl_rq(dl_rq), 1); > + > + if (!dl_server(dl_se)) > + sub_nr_running(rq_of_dl_rq(dl_rq), 1); > > dec_dl_deadline(dl_rq, dl_se->deadline); > } This seems to make sense to me. Thanks for the analysis and the patch. Peter, what do you think? Thanks, Juri