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Message-ID: <87ppd984qv.fsf@rustcorp.com.au>
Date: Fri, 31 Oct 2014 10:55:28 +1030
From: Rusty Russell <rusty@...tcorp.com.au>
To: Prarit Bhargava <prarit@...hat.com>
Cc: linux-kernel@...r.kernel.org, Jonathan Corbet <corbet@....net>,
Andrew Morton <akpm@...ux-foundation.org>,
"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, linux-doc@...r.kernel.org,
kexec@...ts.infradead.org, linux-api@...r.kernel.org
Subject: Re: [PATCH V2] kernel, add bug_on_warn
Prarit Bhargava <prarit@...hat.com> writes:
> On 10/22/2014 12:27 AM, Rusty Russell wrote:
>> Prarit Bhargava <prarit@...hat.com> writes:
>>> There have been several times where I have had to rebuild a kernel to
>>> cause a panic when hitting a WARN() in the code in order to get a crash
>>> dump from a system. Sometimes this is easy to do, other times (such as
>>> in the case of a remote admin) it is not trivial to send new images to the
>>> user.
>>
>> What about during early boot?
>
> Hi Rusty,
>
> I really don't have a use case for this in early boot. The kernel boots, the
> initramfs, and then we run whatever init (systemd in my case). A systemd script
> configures kexec for kdump and that point kdump is "armed". Doing a bug_on_warn
> before this will simply result in a panicked system. I don't get any "new"
> information FWIW as I get a stack trace, etc., in both the WARN() and BUG() cases.
>
>>
>> I'd recommend you use core_param(). Less code, and can be set on
>> commandline.
>
> Is that a general request, or is it dependent on the answer above? Of course I
> have no problem doing it either way.
Oops, I read your initial patch too lightly: I see you added both
a sysctl (which I saw) and an early_param (which I didn't).
I still think it should be a core_param, like so (untested!):
diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt
index 6c0b9f27e465..cf16cbe9f544 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, bug_on_warn, calls BUG() in all WARN() paths. This
+will cause a kdump to occur at the BUG() call. In cases where a user
+wants to specify this during runtime, /sys/module/kernel/bug_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 74339c57b914..aa1d3198e987 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -553,6 +553,9 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
bttv.pll= See Documentation/video4linux/bttv/Insmod-options
bttv.tuner=
+ bug_on_warn BUG() instead of WARN(). Useful to cause kdump
+ on a WARN().
+
bulk_remove=off [PPC] This parameter disables the use of the pSeries
firmware feature for flushing multiple hpte entries
at a time.
diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h
index 630dd2372238..4d0c763862b0 100644
--- a/include/asm-generic/bug.h
+++ b/include/asm-generic/bug.h
@@ -75,10 +75,18 @@ extern void warn_slowpath_null(const char *file, const int line);
#define __WARN_printf_taint(taint, arg...) \
warn_slowpath_fmt_taint(__FILE__, __LINE__, taint, arg)
#else
-#define __WARN() __WARN_TAINT(TAINT_WARN)
+#define check_bug_on_warn() \
+ do { \
+ if (bug_on_warn) \
+ BUG(); \
+ } while (0)
+
+#define __WARN() \
+ do { __WARN_TAINT(TAINT_WARN); check_bug_on_warn(); } while (0)
+
#define __WARN_printf(arg...) do { printk(arg); __WARN(); } while (0)
#define __WARN_printf_taint(taint, arg...) \
- do { printk(arg); __WARN_TAINT(taint); } while (0)
+ do { printk(arg); __WARN_TAINT(taint); check_bug_on_warn(); } while (0)
#endif
#ifndef WARN_ON
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 3d770f5564b8..d583df09ee82 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -423,6 +423,7 @@ extern int panic_on_oops;
extern int panic_on_unrecovered_nmi;
extern int panic_on_io_nmi;
extern int sysctl_panic_on_stackoverflow;
+extern bool bug_on_warn;
/*
* Only to be used by arch init code. If the user over-wrote the default
* CONFIG_PANIC_TIMEOUT, honor it.
diff --git a/kernel/panic.c b/kernel/panic.c
index d09dc5c32c67..3d345357fcc8 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;
+bool bug_on_warn;
int panic_timeout = CONFIG_PANIC_TIMEOUT;
EXPORT_SYMBOL_GPL(panic_timeout);
@@ -420,13 +421,24 @@ static void warn_slowpath_common(const char *file, int line, void *caller,
{
disable_trace_on_warning();
- pr_warn("------------[ cut here ]------------\n");
+ if (!bug_on_warn)
+ pr_warn("------------[ cut here ]------------\n");
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 (bug_on_warn) {
+ pr_warn("bug_on_warn set, calling BUG()...\n");
+ /*
+ * A flood of WARN()s may occur. Prevent further WARN()s
+ * from panicking the system.
+ */
+ bug_on_warn = false;
+ BUG();
+ }
+
print_modules();
dump_stack();
print_oops_end_marker();
@@ -484,6 +496,7 @@ EXPORT_SYMBOL(__stack_chk_fail);
core_param(panic, panic_timeout, int, 0644);
core_param(pause_on_oops, pause_on_oops, int, 0644);
+core_param(bug_on_warn, bug_on_warn, bool, 0644);
static int __init setup_crash_kexec_post_notifiers(char *s)
{
--
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