lkml.org 
[lkml]   [2015]   [Sep]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[RFC v0 9/9] doc: Update cpu-hotplug documents on removal of CPU_TASKS_FROZEN
Date
CPU_*_FROZEN states are gone update the documentation accordingly.

I am not completely convinced that the listed known race condition
can be removed as it is done in this patch. If a suspend/resume is
ongoing while cpu_{down|up}() is called renders at least the 'always
passing 0 as tasks_frozen in cpu_up()' argument false.

Signed-off-by: Daniel Wagner <daniel.wagner@bmw-carit.de>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Len Brown <len.brown@intel.com>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
---
Documentation/cpu-hotplug.txt | 12 +++++-------
Documentation/fault-injection/notifier-error-inject.txt | 2 --
Documentation/power/suspend-and-cpuhotplug.txt | 13 ++-----------
3 files changed, 7 insertions(+), 20 deletions(-)

diff --git a/Documentation/cpu-hotplug.txt b/Documentation/cpu-hotplug.txt
index f9ad5e0..e362f42 100644
--- a/Documentation/cpu-hotplug.txt
+++ b/Documentation/cpu-hotplug.txt
@@ -244,9 +244,9 @@ Q: What happens when a CPU is being logically offlined?
A: The following happen, listed in no particular order :-)

- A notification is sent to in-kernel registered modules by sending an event
- CPU_DOWN_PREPARE or CPU_DOWN_PREPARE_FROZEN, depending on whether or not the
- CPU is being offlined while tasks are frozen due to a suspend operation in
- progress
+ CPU_DOWN_PREPARE. Via freeze_active it is possible to inquire if a suspend
+ operation is ongoing, that is a CPU is beeing offlined while tasks
+ are frozen.
- All processes are migrated away from this outgoing CPU to new CPUs.
The new CPU is chosen from each process' current cpuset, which may be
a subset of all online CPUs.
@@ -255,8 +255,8 @@ A: The following happen, listed in no particular order :-)
- Once all services are migrated, kernel calls an arch specific routine
__cpu_disable() to perform arch specific cleanup.
- Once this is successful, an event for successful cleanup is sent by an event
- CPU_DEAD (or CPU_DEAD_FROZEN if tasks are frozen due to a suspend while the
- CPU is being offlined).
+ CPU_DEAD (if tasks are frozen due to a suspend while the
+ CPU is being offlined can be probed via freeze_active()).

"It is expected that each service cleans up when the CPU_DOWN_PREPARE
notifier is called, when CPU_DEAD is called its expected there is nothing
@@ -274,11 +274,9 @@ A: This is what you would need in your kernel code to receive notifications.

switch (action) {
case CPU_ONLINE:
- case CPU_ONLINE_FROZEN:
foobar_online_action(cpu);
break;
case CPU_DEAD:
- case CPU_DEAD_FROZEN:
foobar_dead_action(cpu);
break;
}
diff --git a/Documentation/fault-injection/notifier-error-inject.txt b/Documentation/fault-injection/notifier-error-inject.txt
index 09adabe..1ec4e84 100644
--- a/Documentation/fault-injection/notifier-error-inject.txt
+++ b/Documentation/fault-injection/notifier-error-inject.txt
@@ -23,9 +23,7 @@ the error code to debugfs interface
Possible CPU notifier events to be failed are:

* CPU_UP_PREPARE
- * CPU_UP_PREPARE_FROZEN
* CPU_DOWN_PREPARE
- * CPU_DOWN_PREPARE_FROZEN

Example1: Inject CPU offline error (-1 == -EPERM)

diff --git a/Documentation/power/suspend-and-cpuhotplug.txt b/Documentation/power/suspend-and-cpuhotplug.txt
index 2fc9095..ab657cd 100644
--- a/Documentation/power/suspend-and-cpuhotplug.txt
+++ b/Documentation/power/suspend-and-cpuhotplug.txt
@@ -232,7 +232,7 @@ d. Handling microcode update during suspend/hibernate:
hibernate/restore cycle.]

In the current design of the kernel however, during a CPU offline operation
- as part of the suspend/hibernate cycle (the CPU_DEAD_FROZEN notification),
+ as part of the suspend/hibernate cycle (see freeze_active()),
the existing copy of microcode image in the kernel is not freed up.
And during the CPU online operations (during resume/restore), since the
kernel finds that it already has copies of the microcode images for all the
@@ -248,16 +248,7 @@ III. Are there any known problems when regular CPU hotplug and suspend race

Yes, they are listed below:

-1. When invoking regular CPU hotplug, the 'tasks_frozen' argument passed to
- the _cpu_down() and _cpu_up() functions is *always* 0.
- This might not reflect the true current state of the system, since the
- tasks could have been frozen by an out-of-band event such as a suspend
- operation in progress. Hence, it will lead to wrong notifications being
- sent during the cpu online/offline events (eg, CPU_ONLINE notification
- instead of CPU_ONLINE_FROZEN) which in turn will lead to execution of
- inappropriate code by the callbacks registered for such CPU hotplug events.
-
-2. If a regular CPU hotplug stress test happens to race with the freezer due
+1. If a regular CPU hotplug stress test happens to race with the freezer due
to a suspend operation in progress at the same time, then we could hit the
situation described below:

--
2.4.3


\
 
 \ /
  Last update: 2015-09-04 16:01    [W:0.123 / U:0.452 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site