Hi Ingo,
On Thursday 14 January 2016 03:39 PM, Ingo Molnar wrote:
* Keerthy <a0393675@xxxxxx> wrote:
Hi Ingo,
On Thursday 14 January 2016 02:35 PM, Ingo Molnar wrote:
* Keerthy <j-keerthy@xxxxxx> wrote:
orderly_poweroff is triggered when a graceful shutdown
of system is desired. This may be used in many critical states of the
kernel such as when subsystems detects conditions such as critical
temperature conditions. However, in certain conditions in system
boot up sequences like those in the middle of driver probes being
initiated, userspace will be unable to power off the system in a clean
manner and leaves the system in a critical state. In cases like these,
the /sbin/poweroff will return success (having forked off to attempt
powering off the system. However, the system overall will fail to
completely poweroff (since other modules will be probed) and the system
is still functional with no userspace (since that would have shut itself
off).
However, there is no clean way of detecting such failure of userspace
powering off the system. In such scenarios, it is necessary for a backup
workqueue to be able to force a shutdown of the system when orderly
shutdown is not successful after a configurable time period.
Signed-off-by: Keerthy <j-keerthy@xxxxxx>
Suggested-by: Eduardo Valentin <edubezval@xxxxxxxxx>
Reported-by: Nishanth Menon <nm@xxxxxx>
---
Links to previous discussion can be found here:
http://www.spinics.net/lists/linux-omap/msg124925.html
Boot tested on DRA7.
changes in v2:
* Changed #ifdef to #if CONFIG_SHUTDOWN_BACKUP_DELAY_MS
arch/Kconfig | 7 +++++++
kernel/reboot.c | 23 ++++++++++++++++++-----
2 files changed, 25 insertions(+), 5 deletions(-)
Index: linux/arch/Kconfig
===================================================================
--- linux.orig/arch/Kconfig 2016-01-11 15:26:07.732173131 +0530
+++ linux/arch/Kconfig 2016-01-11 15:26:07.728173205 +0530
@@ -37,6 +37,18 @@
def_bool y
depends on PERF_EVENTS && HAVE_PERF_EVENTS_NMI && !PPC64
+config SHUTDOWN_BACKUP_DELAY_MS
+ int "Backup shutdown delay in milli-seconds"
+ default 0
+ help
+ The number of milliseconds to delay before backup workqueue
+ executes attempting to poweroff the system after the
+ orderly_poweroff function has failed to complete.
+
+ If set to 0, the backup workqueue is not active. The value
+ should be conservatively configured based on userspace latencies
+ expected for a given system.
I don't really understand this. In what circumstances can a reboot fail?
I think that is what should be fixed: a reboot should never fail, instead of
introducing some sort of fragile timeout based method.
Here is the complete description of the scenario which was reported by Nishanth
who encountered the issue. The link has bootlogs and description of the exact
case which led to this patch.
http://www.spinics.net/lists/linux-omap/msg124923.html
it's a reply in the middle of a discussion ...
What I managed to decode is that this:
static int __orderly_poweroff(bool force)
{
int ret;
ret = run_cmd(poweroff_cmd);
if (ret && force) {
pr_warn("Failed to start orderly shutdown: forcing the issue\n");
/*
* I guess this should try to kick off some daemon to sync and
* poweroff asap. Or not even bother syncing if we're doing an
* emergency shutdown?
*/
emergency_sync();
kernel_power_off();
}
return ret;
}
could fail to actually power the system off, if the run_cmd(poweroff_cmd)
'succeeds', but due to a user-space bug it does not actually call the real
poweroff system call?
I tried to simulate the issue.
In the probe function of drivers/thermal/ti-soc-thermal/ti-bandgap.c
ti_bandgap_probe i call
orderly_poweroff(true);
This is while driver probes are still on going. I observe that
ret = run_cmd(poweroff_cmd);
ret is a non-zero value and we enter the if condition:
Even after the
emergency_sync();
kernel_power_off();
calls
the console remained active in weird state.
Thanks,
Ingo
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