linux-kernel - Re: [PATCH 1/3] sched/deadline: Fix warning in migrate

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Message-ID: <Zp9uzXUwbJOpuwsv@jlelli-thinkpadt14gen4.remote.csb>
Date: Tue, 23 Jul 2024 10:50:21 +0200
From: Juri Lelli <juri.lelli@...hat.com>
To: Wander Lairson Costa <wander@...hat.com>
Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
	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>,
	"open list:SCHEDULER" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] sched/deadline: Fix warning in migrate_enable for
 boosted tasks

Hi Wander,

On 22/07/24 10:29, Wander Lairson Costa wrote:
> When running the following command:
> 
> while true; do
>     stress-ng --cyclic 30 --timeout 30s --minimize --quiet
> done
> 
> a warning is eventually triggered:
> 
> WARNING: CPU: 43 PID: 2848 at kernel/sched/deadline.c:794
> setup_new_dl_entity+0x13e/0x180
> ...
> Call Trace:
>  <TASK>
>  ? show_trace_log_lvl+0x1c4/0x2df
>  ? enqueue_dl_entity+0x631/0x6e0
>  ? setup_new_dl_entity+0x13e/0x180
>  ? __warn+0x7e/0xd0
>  ? report_bug+0x11a/0x1a0
>  ? handle_bug+0x3c/0x70
>  ? exc_invalid_op+0x14/0x70
>  ? asm_exc_invalid_op+0x16/0x20
>  enqueue_dl_entity+0x631/0x6e0
>  enqueue_task_dl+0x7d/0x120
>  __do_set_cpus_allowed+0xe3/0x280
>  __set_cpus_allowed_ptr_locked+0x140/0x1d0
>  __set_cpus_allowed_ptr+0x54/0xa0
>  migrate_enable+0x7e/0x150
>  rt_spin_unlock+0x1c/0x90
>  group_send_sig_info+0xf7/0x1a0
>  ? kill_pid_info+0x1f/0x1d0
>  kill_pid_info+0x78/0x1d0
>  kill_proc_info+0x5b/0x110
>  __x64_sys_kill+0x93/0xc0
>  do_syscall_64+0x5c/0xf0
>  entry_SYSCALL_64_after_hwframe+0x6e/0x76
>  RIP: 0033:0x7f0dab31f92b
> 
> This warning occurs because set_cpus_allowed dequeues and enqueues tasks
> with the ENQUEUE_RESTORE flag set. If the task is boosted, the warning
> is triggered. A boosted task already had its parameters set by
> rt_mutex_setprio, and a new call to setup_new_dl_entity is unnecessary,
> hence the WARN_ON call.
> 
> Check if we are requeueing a boosted task and avoid calling
> setup_new_dl_entity if that's the case.
> 
> Signed-off-by: Wander Lairson Costa <wander@...hat.com>
> Fixes: 2279f540ea7d ("sched/deadline: Fix priority inheritance with multiple scheduling classes")

I believe your fix makes sense to me. I only wonder if however it
actually fixes 295d6d5e37360 ("sched/deadline: Fix switching to
-deadline") instead of the change you reference above?

Thanks,
Juri