Freezer: make kernel threads nonfreezable by default

Currently, the freezer treats all tasks as freezable, except for the kernel
threads that explicitly set the PF_NOFREEZE flag for themselves.  This
approach is problematic, since it requires every kernel thread to either
set PF_NOFREEZE explicitly, or call try_to_freeze(), even if it doesn't
care for the freezing of tasks at all.

It seems better to only require the kernel threads that want to or need to
be frozen to use some freezer-related code and to remove any
freezer-related code from the other (nonfreezable) kernel threads, which is
done in this patch.

The patch causes all kernel threads to be nonfreezable by default (ie.  to
have PF_NOFREEZE set by default) and introduces the set_freezable()
function that should be called by the freezable kernel threads in order to
unset PF_NOFREEZE.  It also makes all of the currently freezable kernel
threads call set_freezable(), so it shouldn't cause any (intentional)
change of behaviour to appear.  Additionally, it updates documentation to
describe the freezing of tasks more accurately.

[akpm@linux-foundation.org: build fixes]
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Nigel Cunningham <nigel@nigel.suspend2.net>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Gautham R Shenoy <ego@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 2 deletions

diff --git a/drivers/media/video/msp3400-kthreads.c b/drivers/media/video/msp3400-kthreads.c
index e1821eb82fb5..d5ee2629121e 100644
--- a/drivers/media/video/msp3400-kthreads.c
+++ b/drivers/media/video/msp3400-kthreads.c
@@ -23,6 +23,7 @@
 #include <linux/module.h>
 #include <linux/slab.h>
 #include <linux/i2c.h>
+#include <linux/freezer.h>
 #include <linux/videodev.h>
 #include <linux/videodev2.h>
 #include <media/v4l2-common.h>
@@ -468,6 +469,7 @@ int msp3400c_thread(void *data)
 
 
         v4l_dbg(1, msp_debug, client, "msp3400 daemon started\n");
+        set_freezable();
         for (;;) {
                 v4l_dbg(2, msp_debug, client, "msp3400 thread: sleep\n");
                 msp_sleep(state, -1);
@@ -646,7 +648,7 @@ int msp3410d_thread(void *data)
         int val, i, std, count;
 
         v4l_dbg(1, msp_debug, client, "msp3410 daemon started\n");
-
+        set_freezable();
         for (;;) {
                 v4l_dbg(2, msp_debug, client, "msp3410 thread: sleep\n");
                 msp_sleep(state,-1);
@@ -940,7 +942,7 @@ int msp34xxg_thread(void *data)
         int val, i;
 
         v4l_dbg(1, msp_debug, client, "msp34xxg daemon started\n");
-
+        set_freezable();
         for (;;) {
                 v4l_dbg(2, msp_debug, client, "msp34xxg thread: sleep\n");
                 msp_sleep(state, -1);