Re: [PATCH 1/3] sched/deadline: Fix warning in migrate_enable for boosted tasks

From: Juri Lelli
Date: Tue Jul 23 2024 - 04:51:21 EST


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@xxxxxxxxxx>
> 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