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Date: Wed, 5 Nov 2014 13:59:18 -0800 (PST)
From: David Rientjes <rientjes@...gle.com>
To: Prarit Bhargava <prarit@...hat.com>
cc: linux-kernel@...r.kernel.org, Jonathan Corbet <corbet@....net>,
Andrew Morton <akpm@...ux-foundation.org>,
Rusty Russell <rusty@...tcorp.com.au>,
"H. Peter Anvin" <hpa@...or.com>, Andi Kleen <ak@...ux.intel.com>,
Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
Fabian Frederick <fabf@...net.be>, vgoyal@...hat.com,
isimatu.yasuaki@...fujitsu.com, jbaron@...mai.com,
linux-doc@...r.kernel.org, kexec@...ts.infradead.org,
linux-api@...r.kernel.org
Subject: Re: [PATCH v8] kernel, add panic_on_warn
On Wed, 5 Nov 2014, Prarit Bhargava wrote:
> diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt
> index 6c0b9f2..bc4bd5a 100644
> --- a/Documentation/kdump/kdump.txt
> +++ b/Documentation/kdump/kdump.txt
> @@ -471,6 +471,13 @@ format. Crash is available on Dave Anderson's site at the following URL:
>
> http://people.redhat.com/~anderson/
>
> +Trigger Kdump on WARN()
> +=======================
> +
> +The kernel parameter, panic_on_warn, calls panic() in all WARN() paths. This
> +will cause a kdump to occur at the panic() call. In cases where a user wants
> +to specify this during runtime, /proc/sys/kernel/panic_on_warn can be set to 1
> +to achieve the same behaviour.
>
> Contact
> =======
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 4c81a86..ea5d57c 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -2509,6 +2509,9 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
> timeout < 0: reboot immediately
> Format: <timeout>
>
> + panic_on_warn panic() instead of WARN(). Useful to cause kdump
> + on a WARN().
> +
> crash_kexec_post_notifiers
> Run kdump after running panic-notifiers and dumping
> kmsg. This only for the users who doubt kdump always
> diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
> index 57baff5..b5d0c85 100644
> --- a/Documentation/sysctl/kernel.txt
> +++ b/Documentation/sysctl/kernel.txt
> @@ -54,8 +54,9 @@ show up in /proc/sys/kernel:
> - overflowuid
> - panic
> - panic_on_oops
> -- panic_on_unrecovered_nmi
> - panic_on_stackoverflow
> +- panic_on_unrecovered_nmi
> +- panic_on_warn
> - pid_max
> - powersave-nap [ PPC only ]
> - printk
> @@ -527,19 +528,6 @@ the recommended setting is 60.
>
> ==============================================================
>
> -panic_on_unrecovered_nmi:
> -
> -The default Linux behaviour on an NMI of either memory or unknown is
> -to continue operation. For many environments such as scientific
> -computing it is preferable that the box is taken out and the error
> -dealt with than an uncorrected parity/ECC error get propagated.
> -
> -A small number of systems do generate NMI's for bizarre random reasons
> -such as power management so the default is off. That sysctl works like
> -the existing panic controls already in that directory.
> -
> -==============================================================
> -
> panic_on_oops:
>
> Controls the kernel's behaviour when an oops or BUG is encountered.
> @@ -563,6 +551,30 @@ This file shows up if CONFIG_DEBUG_STACKOVERFLOW is enabled.
>
> ==============================================================
>
> +panic_on_unrecovered_nmi:
> +
> +The default Linux behaviour on an NMI of either memory or unknown is
> +to continue operation. For many environments such as scientific
> +computing it is preferable that the box is taken out and the error
> +dealt with than an uncorrected parity/ECC error get propagated.
> +
> +A small number of systems do generate NMI's for bizarre random reasons
> +such as power management so the default is off. That sysctl works like
> +the existing panic controls already in that directory.
> +
> +==============================================================
> +
> +panic_on_warn:
> +
> +Calls panic() in the WARN() path when set to 1. This is useful to avoid
> +a kernel rebuild when attempting to kdump at the location of a WARN().
> +
> +0: only WARN(), default behaviour.
> +
> +1: call panic() after printing out WARN() location.
> +
> +==============================================================
> +
> 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 3d770f55..d60d31d 100644
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -422,6 +422,7 @@ extern int panic_timeout;
> extern int panic_on_oops;
> extern int panic_on_unrecovered_nmi;
> extern int panic_on_io_nmi;
> +extern int panic_on_warn;
> extern int sysctl_panic_on_stackoverflow;
> /*
> * Only to be used by arch init code. If the user over-wrote the default
> diff --git a/include/uapi/linux/sysctl.h b/include/uapi/linux/sysctl.h
> index 43aaba1..0956373 100644
> --- a/include/uapi/linux/sysctl.h
> +++ b/include/uapi/linux/sysctl.h
> @@ -153,6 +153,7 @@ enum
> KERN_MAX_LOCK_DEPTH=74, /* int: rtmutex's maximum lock depth */
> KERN_NMI_WATCHDOG=75, /* int: enable/disable nmi watchdog */
> KERN_PANIC_ON_NMI=76, /* int: whether we will panic on an unrecovered */
> + KERN_PANIC_ON_WARN=77, /* int: call panic() in WARN() functions */
> };
>
>
> diff --git a/kernel/panic.c b/kernel/panic.c
> index d09dc5c..c6a7723 100644
> --- a/kernel/panic.c
> +++ b/kernel/panic.c
> @@ -33,6 +33,7 @@ static int pause_on_oops;
> static int pause_on_oops_flag;
> static DEFINE_SPINLOCK(pause_on_oops_lock);
> static bool crash_kexec_post_notifiers;
> +int panic_on_warn __read_mostly;
>
> int panic_timeout = CONFIG_PANIC_TIMEOUT;
> EXPORT_SYMBOL_GPL(panic_timeout);
> @@ -420,13 +421,23 @@ static void warn_slowpath_common(const char *file, int line, void *caller,
> {
> disable_trace_on_warning();
>
> - pr_warn("------------[ cut here ]------------\n");
> + if (!panic_on_warn)
> + pr_warn("------------[ cut here ]------------\n");
Is this really necessary?
> pr_warn("WARNING: CPU: %d PID: %d at %s:%d %pS()\n",
> raw_smp_processor_id(), current->pid, file, line, caller);
>
> if (args)
> vprintk(args->fmt, args->args);
>
> + if (panic_on_warn) {
> + /*
> + * A flood of WARN()s may occur. Prevent further WARN()s
> + * from panicking the system.
> + */
What synchronization is preventing this race and further WARN()s panicking
the system?
> + panic_on_warn = 0;
> + panic("panic_on_warn set ...\n");
> + }
> +
> print_modules();
> dump_stack();
> print_oops_end_marker();
--
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