Re: [RFC PATCH 2/2] sched: sysctl: Panic on scheduling while atomic

[Josh Triplett <josh@joshtriplett.org>]

On Tue, May 31, 2016 at 04:07:33PM -0300, Daniel Bristot de Oliveira wrote:
> Currently, a schedule while atomic error prints the stack trace to the
> kernel log and the system continue running.
> 
> Although it is possible to collect the kernel log messages and analyse
> it, often more information are needed. Furthermore, keep the system
> running is not always the best choice. For example, when the preempt
> count underflows the system will not stop to complain about scheduling
> while atomic, so the kernel log can wraparound overwriting the first
> stack trace, tuning the analysis even more difficult.
> 
> This patch implements the kernel.panic_on_sched_in_atomic sysctl to
> help out on these more complex situations.
> 
> When kernel.panic_on_sched_in_atomic is set to 1, the kernel will
> panic() in the schedule while atomic detection.
> 
> The default value for the sysctl is 0, maintaining the current behavior.
> 
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Reviewed-by: Arnaldo Carvalho de Melo <acme@kernel.org>
> Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>

Reviewed-by: Josh Triplett <josh@joshtriplett.org>

>  Documentation/sysctl/kernel.txt | 13 +++++++++++++
>  include/linux/kernel.h          |  1 +
>  kernel/sched/core.c             |  7 +++++++
>  kernel/sysctl.c                 |  9 +++++++++
>  4 files changed, 30 insertions(+)
> 
> diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
> index 29ec4bb..0b176bb 100644
> --- a/Documentation/sysctl/kernel.txt
> +++ b/Documentation/sysctl/kernel.txt
> @@ -59,6 +59,7 @@ show up in /proc/sys/kernel:
>  - panic_on_unrecovered_nmi
>  - panic_on_warn
>  - panic_on_rcu_stall
> +- panic_on_sched_in_atomic
>  - perf_cpu_time_max_percent
>  - perf_event_paranoid
>  - perf_event_max_stack
> @@ -630,6 +631,18 @@ is useful to define the root cause of RCU stalls using kdump.
>  
>  ==============================================================
>  
> +panic_on_sched_in_atomic:
> +
> +When set to 1, calls panic() in the schedule while in atomic detection.
> +This is useful get a vmcore to inspect the root cause of a schedule()
> +call in the atomic context.
> +
> +0: do not panic() on scheduling while in atomic, default behavior.
> +
> +1: panic() after printing schedule while in atomic messages.
> +
> +==============================================================
> +
>  perf_cpu_time_max_percent:
>  
>  Hints to the kernel how much CPU time it should be allowed to
> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> index c420821..e4d9804 100644
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -452,6 +452,7 @@ extern int panic_on_unrecovered_nmi;
>  extern int panic_on_io_nmi;
>  extern int panic_on_warn;
>  extern int sysctl_panic_on_rcu_stall;
> +extern int sysctl_panic_on_sched_in_atomic;
>  extern int sysctl_panic_on_stackoverflow;
>  
>  extern bool crash_kexec_post_notifiers;
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 7f2cae4..602f978 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -152,6 +152,11 @@ __read_mostly int scheduler_running;
>   */
>  int sysctl_sched_rt_runtime = 950000;
>  
> +/*
> + * panic on scheduling while atomic
> + */
> +__read_mostly int sysctl_panic_on_sched_in_atomic = 0;
> +
>  /* cpus with isolated domains */
>  cpumask_var_t cpu_isolated_map;
>  
> @@ -3146,6 +3151,8 @@ static noinline void __schedule_bug(struct task_struct *prev)
>  		pr_cont("\n");
>  	}
>  #endif
> +	if (sysctl_panic_on_sched_in_atomic)
> +		panic("scheduling while atomic\n");
>  	dump_stack();
>  	add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
>  }
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index d3b93aa..f0a984c 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -1216,6 +1216,15 @@ static struct ctl_table kern_table[] = {
>  		.extra2		= &one,
>  	},
>  #endif
> +	{
> +		.procname	= "panic_on_sched_in_atomic",
> +		.data		= &sysctl_panic_on_sched_in_atomic,
> +		.maxlen		= sizeof(sysctl_panic_on_sched_in_atomic),
> +		.mode		= 0644,
> +		.proc_handler	= proc_dointvec_minmax,
> +		.extra1		= &zero,
> +		.extra2		= &one,
> +	},
>  	{ }
>  };
>  
> -- 
> 2.5.5
>