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authorArnd Bergmann <arnd@arndb.de>2012-05-11 17:15:31 +0200
committerArnd Bergmann <arnd@arndb.de>2012-05-11 17:15:31 +0200
commit93c6d8927fa692faef3d7d945bd4fe84b0185ad4 (patch)
tree0a971c86114656ec4e39f7789d9faeb70432c36a /Documentation/power/freezing-of-tasks.txt
parentea01d31a07ae182028d2398380948f5a4ee09953 (diff)
parent50260924afd4b745bfb6e5f1caee381a1875fc31 (diff)
Merge branch 'clk/mxs' of git://git.linaro.org/people/shawnguo/linux-2.6 into next/clock
Shawn Guo <shawn.guo@linaro.org> writes: mxs common clk porting for v3.5. It depends on the following two branches. [1] git://git.linaro.org/people/mturquette/linux.git clk-next [2] http://ftp.arm.linux.org.uk/pub/linux/arm/kernel/git-cur/linux-arm.git clkdev As the mxs device tree conversion will constantly touch clock files, to save the conflicts, the updated mxs/dt branch coming later will based on this pull-request. * 'clk/mxs' of git://git.linaro.org/people/shawnguo/linux-2.6: ARM: mxs: remove now unused timer_clk argument from mxs_timer_init ARM: mxs: remove old clock support ARM: mxs: switch to common clk framework ARM: mxs: change the lookup name for fec phy clock ARM: mxs: request clock for timer clk: mxs: add clock support for imx28 clk: mxs: add clock support for imx23 clk: mxs: add mxs specific clocks Includes an update to Linux 3.4-rc6 Conflicts: drivers/clk/Makefile Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Diffstat (limited to 'Documentation/power/freezing-of-tasks.txt')
-rw-r--r--Documentation/power/freezing-of-tasks.txt37
1 files changed, 19 insertions, 18 deletions
diff --git a/Documentation/power/freezing-of-tasks.txt b/Documentation/power/freezing-of-tasks.txt
index ec715cd78fb..6ec291ea1c7 100644
--- a/Documentation/power/freezing-of-tasks.txt
+++ b/Documentation/power/freezing-of-tasks.txt
@@ -9,7 +9,7 @@ architectures).
II. How does it work?
-There are four per-task flags used for that, PF_NOFREEZE, PF_FROZEN, TIF_FREEZE
+There are three per-task flags used for that, PF_NOFREEZE, PF_FROZEN
and PF_FREEZER_SKIP (the last one is auxiliary). The tasks that have
PF_NOFREEZE unset (all user space processes and some kernel threads) are
regarded as 'freezable' and treated in a special way before the system enters a
@@ -17,30 +17,31 @@ suspend state as well as before a hibernation image is created (in what follows
we only consider hibernation, but the description also applies to suspend).
Namely, as the first step of the hibernation procedure the function
-freeze_processes() (defined in kernel/power/process.c) is called. It executes
-try_to_freeze_tasks() that sets TIF_FREEZE for all of the freezable tasks and
-either wakes them up, if they are kernel threads, or sends fake signals to them,
-if they are user space processes. A task that has TIF_FREEZE set, should react
-to it by calling the function called __refrigerator() (defined in
-kernel/freezer.c), which sets the task's PF_FROZEN flag, changes its state
-to TASK_UNINTERRUPTIBLE and makes it loop until PF_FROZEN is cleared for it.
-Then, we say that the task is 'frozen' and therefore the set of functions
-handling this mechanism is referred to as 'the freezer' (these functions are
-defined in kernel/power/process.c, kernel/freezer.c & include/linux/freezer.h).
-User space processes are generally frozen before kernel threads.
+freeze_processes() (defined in kernel/power/process.c) is called. A system-wide
+variable system_freezing_cnt (as opposed to a per-task flag) is used to indicate
+whether the system is to undergo a freezing operation. And freeze_processes()
+sets this variable. After this, it executes try_to_freeze_tasks() that sends a
+fake signal to all user space processes, and wakes up all the kernel threads.
+All freezable tasks must react to that by calling try_to_freeze(), which
+results in a call to __refrigerator() (defined in kernel/freezer.c), which sets
+the task's PF_FROZEN flag, changes its state to TASK_UNINTERRUPTIBLE and makes
+it loop until PF_FROZEN is cleared for it. Then, we say that the task is
+'frozen' and therefore the set of functions handling this mechanism is referred
+to as 'the freezer' (these functions are defined in kernel/power/process.c,
+kernel/freezer.c & include/linux/freezer.h). User space processes are generally
+frozen before kernel threads.
__refrigerator() must not be called directly. Instead, use the
try_to_freeze() function (defined in include/linux/freezer.h), that checks
-the task's TIF_FREEZE flag and makes the task enter __refrigerator() if the
-flag is set.
+if the task is to be frozen and makes the task enter __refrigerator().
For user space processes try_to_freeze() is called automatically from the
signal-handling code, but the freezable kernel threads need to call it
explicitly in suitable places or use the wait_event_freezable() or
wait_event_freezable_timeout() macros (defined in include/linux/freezer.h)
-that combine interruptible sleep with checking if TIF_FREEZE is set and calling
-try_to_freeze(). The main loop of a freezable kernel thread may look like the
-following one:
+that combine interruptible sleep with checking if the task is to be frozen and
+calling try_to_freeze(). The main loop of a freezable kernel thread may look
+like the following one:
set_freezable();
do {
@@ -53,7 +54,7 @@ following one:
(from drivers/usb/core/hub.c::hub_thread()).
If a freezable kernel thread fails to call try_to_freeze() after the freezer has
-set TIF_FREEZE for it, the freezing of tasks will fail and the entire
+initiated a freezing operation, the freezing of tasks will fail and the entire
hibernation operation will be cancelled. For this reason, freezable kernel
threads must call try_to_freeze() somewhere or use one of the
wait_event_freezable() and wait_event_freezable_timeout() macros.