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Groups > linux.kernel > #1219003

[RFC v0 9/9] doc: Update cpu-hotplug documents on removal of CPU_TASKS_FROZEN

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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

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[RFC v0 0/9] Remove CPU_*_FROZEN Daniel Wagner <daniel.wagner@bmw-carit.de> - 2015-09-04 15:40 +0200
  [RFC v0 8/9] cpu: Do not set CPU_TASKS_FROZEN anymore Daniel Wagner <daniel.wagner@bmw-carit.de> - 2015-09-04 15:40 +0200
  [RFC v0 1/9] smpboot: Add a separate CPU state when a surviving CPU times out Daniel Wagner <daniel.wagner@bmw-carit.de> - 2015-09-04 15:40 +0200
  [RFC v0 2/9] suspend: Add getter function to report if freezing is active Daniel Wagner <daniel.wagner@bmw-carit.de> - 2015-09-04 15:40 +0200
    Re: [RFC v0 2/9] suspend: Add getter function to report if freezing is active "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2015-09-05 03:50 +0200
  [RFC v0 5/9] sched: Use freeze_active() instead CPU_*_FROZEN state information Daniel Wagner <daniel.wagner@bmw-carit.de> - 2015-09-04 15:40 +0200
  [RFC v0 4/9] smpboot: Use freeze_active() instead CPU_DEAD_FROZEN state information Daniel Wagner <daniel.wagner@bmw-carit.de> - 2015-09-04 15:40 +0200
  [RFC v0 6/9] cpu: Restructure FROZEN state handling Daniel Wagner <daniel.wagner@bmw-carit.de> - 2015-09-04 15:40 +0200
  [RFC v0 3/9] x86: Use freeze_active() instead of CPU_*_FROZEN Daniel Wagner <daniel.wagner@bmw-carit.de> - 2015-09-04 15:40 +0200
  [RFC v0 9/9] doc: Update cpu-hotplug documents on removal of CPU_TASKS_FROZEN Daniel Wagner <daniel.wagner@bmw-carit.de> - 2015-09-04 15:40 +0200

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