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[79.23.205.114]) by smtp.gmail.com with ESMTPSA id n2sm9701405edi.32.2021.06.28.09.25.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 28 Jun 2021 09:25:47 -0700 (PDT) Subject: Re: [PATCH] tracing: Have osnoise_main() add a quiescent state for task rcu To: Steven Rostedt , LKML Cc: "Paul E. McKenney" , Ingo Molnar References: <20210628114953.6dc06a91@oasis.local.home> From: Daniel Bristot de Oliveira Message-ID: <8f16ef64-b06e-b3bf-4b6f-8fc4a15b2801@redhat.com> Date: Mon, 28 Jun 2021 18:25:43 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210628114953.6dc06a91@oasis.local.home> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/28/21 5:49 PM, Steven Rostedt wrote: > From: "Steven Rostedt (VMware)" > > ftracetest triggered: > > INFO: rcu_tasks detected stalls on tasks: > 00000000b92b832d: .. nvcsw: 1/1 holdout: 1 idle_cpu: -1/7 > task:osnoise/7 state:R running task stack: 0 pid: 2133 ppid: 2 flags:0x00004000 > Call Trace: > ? asm_sysvec_apic_timer_interrupt+0x12/0x20 > ? asm_sysvec_apic_timer_interrupt+0x12/0x20 > ? trace_hardirqs_on+0x2b/0xe0 > ? asm_sysvec_apic_timer_interrupt+0x12/0x20 > ? trace_clock_local+0xc/0x20 > ? osnoise_main+0x10e/0x450 > ? trace_softirq_entry_callback+0x50/0x50 > ? kthread+0x153/0x170 > ? __kthread_bind_mask+0x60/0x60 > ? ret_from_fork+0x22/0x30 > > While running osnoise tracer with other tracers that rely on > synchronize_rcu_tasks(), where that just hung. > > The reason is that osnoise_main() never schedules out if the interval > is less than 1, and there is no other task setting need resched (it has a regular cond_resched() on the run_osnoise() loop). and this will cause synchronize_rcu_tasks() to never > return. > > Fixes: bce29ac9ce0bb ("trace: Add osnoise tracer") > Signed-off-by: Steven Rostedt (VMware) Reviewed-by: Daniel Bristot de Oliveira Thanks! -- Daniel > --- > kernel/trace/trace_osnoise.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c > index 38aa5e208ffd..556d530af805 100644 > --- a/kernel/trace/trace_osnoise.c > +++ b/kernel/trace/trace_osnoise.c > @@ -1216,8 +1216,11 @@ static int osnoise_main(void *data) > * differently from hwlat_detector, the osnoise tracer can run > * without a pause because preemption is on. > */ > - if (interval < 1) > + if (interval < 1) { > + /* Let synchronize_rcu_tasks() make progress */ > + cond_resched_tasks_rcu_qs(); > continue; > + } > > if (msleep_interruptible(interval)) > break; >