[PATCH 1/2] panic: panic=-1 for immediate reboot

[PATCH 1/2] panic: panic=-1 for immediate reboot

[Mandeep Singh Baines]

From: Hugh Dickins <hughd@chromium.org>

When kernel BUG or oops occurs, ChromeOS intends to panic and immediately
reboot, with stacktrace and other messages preserved in RAM across reboot.
But the longer we delay, the more likely the user is to poweroff and lose
the info.

panic_timeout (seconds before rebooting) is set by panic= boot option
or sysctl or /proc/sys/kernel/panic; but 0 means wait forever, so at
present we have to delay at least 1 second.

Let a negative number mean reboot immediately (with the small cosmetic
benefit of suppressing that newline-less "Rebooting in %d seconds.."
message).

Signed-off-by: Hugh Dickins <hughd@chromium.org>
Signed-off-by: Mandeep Singh Baines <msb@chromium.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Olaf Hering <olaf@aepfle.de>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Cc: Dave Airlie <airlied@gmail.com>
Cc: Greg Kroah-Hartman <gregkh@suse.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
---
 Documentation/kernel-parameters.txt |    4 +++-
 kernel/panic.c                      |    2 ++
 2 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index aa47be7..4f42fc7 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1846,7 +1846,9 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			See Documentation/sound/oss/oss-parameters.txt
 
 	panic=		[KNL] Kernel behaviour on panic: delay <timeout>
-			seconds before rebooting
+			timeout > 0: seconds before rebooting
+			timeout = 0: wait forever
+			timeout < 0: reboot immediately
 			Format: <timeout>
 
 	parkbd.port=	[HW] Parallel port number the keyboard adapter is
diff --git a/kernel/panic.c b/kernel/panic.c
index 6923167..d7bb697 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -119,6 +119,8 @@ NORET_TYPE void panic(const char * fmt, ...)
 			}
 			mdelay(PANIC_TIMER_STEP);
 		}
+	}
+	if (panic_timeout != 0) {
 		/*
 		 * This will not be a clean reboot, with everything
 		 * shutting down.  But if there is a chance of
-- 
1.7.3.1

[PATCH 2/2] panic, vt: do not force oops output when panic_timeout < 0

[Mandeep Singh Baines]

Don't force output if you intend to reboot immediately.

In this patch, I'm disabling the functionality enabled by
vc->vc_panic_force_write if panic_timeout < 0 (i.e. no timeout).
vc_panic_force_write is only enabled for fb video consoles if the
FBINFO_CAN_FORCE_OUTPUT flag is set.

For our application, we're using ram_oops to preserved the panic in memory.
We want to reliably, and as fast as possible, machine_restart. The
vc_panic_force_write flag results in a bunch of graphics driver code to be
invoked which slows down restart and decreases reliability. Since we're
already storing the panic in RAM and are going to reboot immediately, there
is no benefit in mode switching back to the vc in order to display the panic
output. The log buffer will get flushed by the console_unblank() call so
remote management consoles should see all output.

Signed-off-by: Mandeep Singh Baines <msb@chromium.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Olaf Hering <olaf@aepfle.de>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Cc: Dave Airlie <airlied@gmail.com>
Cc: Greg Kroah-Hartman <gregkh@suse.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
---
 include/linux/vt_kern.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/include/linux/vt_kern.h b/include/linux/vt_kern.h
index 4d05e14..c2164fa 100644
--- a/include/linux/vt_kern.h
+++ b/include/linux/vt_kern.h
@@ -137,7 +137,7 @@ int vty_init(const struct file_operations *console_fops);
 
 static inline bool vt_force_oops_output(struct vc_data *vc)
 {
-	if (oops_in_progress && vc->vc_panic_force_write)
+	if (oops_in_progress && vc->vc_panic_force_write  && panic_timeout >= 0)
 		return true;
 	return false;
 }
-- 
1.7.3.1

Re: [PATCH 2/2] panic, vt: do not force oops output when panic_timeout < 0

[Alan Cox]

> already storing the panic in RAM and are going to reboot immediately, there
> is no benefit in mode switching back to the vc in order to display the panic
> output. The log buffer will get flushed by the console_unblank() call so
> remote management consoles should see all output.

Doesn't seem too unreasonable and its probably a behaviour (although with
netconsole) that a lot of server farms would prefer too.

Acked-by: Alan Cox <alan@linux.intel.com>

Re: [PATCH 1/2] panic: panic=-1 for immediate reboot

[Mandeep Singh Baines]

On Fri, Jul 15, 2011 at 3:39 PM, Mandeep Singh Baines <msb@chromium.org> wrote:
> From: Hugh Dickins <hughd@chromium.org>
>
> When kernel BUG or oops occurs, ChromeOS intends to panic and immediately
> reboot, with stacktrace and other messages preserved in RAM across reboot.
> But the longer we delay, the more likely the user is to poweroff and lose
> the info.
>
> panic_timeout (seconds before rebooting) is set by panic= boot option
> or sysctl or /proc/sys/kernel/panic; but 0 means wait forever, so at
> present we have to delay at least 1 second.
>
> Let a negative number mean reboot immediately (with the small cosmetic
> benefit of suppressing that newline-less "Rebooting in %d seconds.."
> message).
>

Ignore this patch. I re-posted the series with documentation updates:

http://lkml.kernel.org/r/1310770401-10739-1-git-send-email-msb@chromium.org

> Signed-off-by: Hugh Dickins <hughd@chromium.org>
> Signed-off-by: Mandeep Singh Baines <msb@chromium.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Huang Ying <ying.huang@intel.com>
> Cc: Andi Kleen <ak@linux.intel.com>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Olaf Hering <olaf@aepfle.de>
> Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
> Cc: Dave Airlie <airlied@gmail.com>
> Cc: Greg Kroah-Hartman <gregkh@suse.de>
> Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
> ---
>  kernel/panic.c |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
>
> diff --git a/kernel/panic.c b/kernel/panic.c
> index 6923167..d7bb697 100644
> --- a/kernel/panic.c
> +++ b/kernel/panic.c
> @@ -119,6 +119,8 @@ NORET_TYPE void panic(const char * fmt, ...)
>                        }
>                        mdelay(PANIC_TIMER_STEP);
>                }
> +       }
> +       if (panic_timeout != 0) {
>                /*
>                 * This will not be a clean reboot, with everything
>                 * shutting down.  But if there is a chance of
> --
> 1.7.3.1
>
>

[PATCH 1/2] panic: panic=-1 for immediate reboot

[Mandeep Singh Baines]

From: Hugh Dickins <hughd@chromium.org>

When kernel BUG or oops occurs, ChromeOS intends to panic and immediately
reboot, with stacktrace and other messages preserved in RAM across reboot.
But the longer we delay, the more likely the user is to poweroff and lose
the info.

panic_timeout (seconds before rebooting) is set by panic= boot option
or sysctl or /proc/sys/kernel/panic; but 0 means wait forever, so at
present we have to delay at least 1 second.

Let a negative number mean reboot immediately (with the small cosmetic
benefit of suppressing that newline-less "Rebooting in %d seconds.."
message).

Signed-off-by: Hugh Dickins <hughd@chromium.org>
Signed-off-by: Mandeep Singh Baines <msb@chromium.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Olaf Hering <olaf@aepfle.de>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Cc: Dave Airlie <airlied@gmail.com>
Cc: Greg Kroah-Hartman <gregkh@suse.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
---
 kernel/panic.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/kernel/panic.c b/kernel/panic.c
index 6923167..d7bb697 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -119,6 +119,8 @@ NORET_TYPE void panic(const char * fmt, ...)
 			}
 			mdelay(PANIC_TIMER_STEP);
 		}
+	}
+	if (panic_timeout != 0) {
 		/*
 		 * This will not be a clean reboot, with everything
 		 * shutting down.  But if there is a chance of
-- 
1.7.3.1

Re: [PATCH 1/2] panic: panic=-1 for immediate reboot

[Mandeep Singh Baines]

On Wed, Jun 22, 2011 at 2:39 AM, Olaf Hering <olaf@aepfle.de> wrote:
> On Mon, Jun 20, Mandeep Singh Baines wrote:
>
>> From: Hugh Dickins <hughd@chromium.org>
>>
>> When kernel BUG or oops occurs, ChromeOS intends to panic and immediately
>> reboot, with stacktrace and other messages preserved in RAM across reboot.
>> But the longer we delay, the more likely the user is to poweroff and lose
>> the info.
>
> I have no strong opinion here, but:
>
> Is delaying one second (instead of say 180 like on powerpc) such a big
> deal if the system is dead anyway?
>

Our kernel is configured to preserve the panic in RAM. So we don't get
any benefit in waiting. On the reboot following the crash, the panic gets
logged. If the user hits the power button instead of waiting for the panic,
we lose the crash data. For this reason, we even set our lockup
thresholds as low as we can.

Our system is almost stateless and our boot time is 8 seconds so a panic
reboot cycle is not so bad. But the quicker we can get the system
back up, the better.

Regards,
Mandeep

> Olaf
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Re: [PATCH 1/2] panic: panic=-1 for immediate reboot

[Olaf Hering]

On Mon, Jun 20, Mandeep Singh Baines wrote:

> From: Hugh Dickins <hughd@chromium.org>
> 
> When kernel BUG or oops occurs, ChromeOS intends to panic and immediately
> reboot, with stacktrace and other messages preserved in RAM across reboot.
> But the longer we delay, the more likely the user is to poweroff and lose
> the info.

I have no strong opinion here, but:

Is delaying one second (instead of say 180 like on powerpc) such a big
deal if the system is dead anyway?

Olaf

[PATCH 1/2] panic: panic=-1 for immediate reboot

[Mandeep Singh Baines]

From: Hugh Dickins <hughd@chromium.org>

When kernel BUG or oops occurs, ChromeOS intends to panic and immediately
reboot, with stacktrace and other messages preserved in RAM across reboot.
But the longer we delay, the more likely the user is to poweroff and lose
the info.

panic_timeout (seconds before rebooting) is set by panic= boot option
or sysctl or /proc/sys/kernel/panic; but 0 means wait forever, so at
present we have to delay at least 1 second.

Let a negative number mean reboot immediately (with the small cosmetic
benefit of suppressing that newline-less "Rebooting in %d seconds.."
message).

Signed-off-by: Hugh Dickins <hughd@chromium.org>
Signed-off-by: Mandeep Singh Baines <msb@chromium.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Hugh Dickins <hughd@chromium.org>
Cc: Olaf Hering <olaf@aepfle.de>
---
 kernel/panic.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/kernel/panic.c b/kernel/panic.c
index 6923167..d7bb697 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -119,6 +119,8 @@ NORET_TYPE void panic(const char * fmt, ...)
 			}
 			mdelay(PANIC_TIMER_STEP);
 		}
+	}
+	if (panic_timeout != 0) {
 		/*
 		 * This will not be a clean reboot, with everything
 		 * shutting down.  But if there is a chance of
-- 
1.7.3.1