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Commit 986b11c3 authored by Rafael J. Wysocki's avatar Rafael J. Wysocki
Browse files

Merge branch 'pm-freezer' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/misc into pm-freezer 

* 'pm-freezer' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/misc: (24 commits)
  freezer: fix wait_event_freezable/__thaw_task races
  freezer: kill unused set_freezable_with_signal()
  dmatest: don't use set_freezable_with_signal()
  usb_storage: don't use set_freezable_with_signal()
  freezer: remove unused @sig_only from freeze_task()
  freezer: use lock_task_sighand() in fake_signal_wake_up()
  freezer: restructure __refrigerator()
  freezer: fix set_freezable[_with_signal]() race
  freezer: remove should_send_signal() and update frozen()
  freezer: remove now unused TIF_FREEZE
  freezer: make freezing() test freeze conditions in effect instead of TIF_FREEZE
  cgroup_freezer: prepare for removal of TIF_FREEZE
  freezer: clean up freeze_processes() failure path
  freezer: kill PF_FREEZING
  freezer: test freezable conditions while holding freezer_lock
  freezer: make freezing indicate freeze condition in effect
  freezer: use dedicated lock instead of task_lock() + memory barrier
  freezer: don't distinguish nosig tasks on thaw
  freezer: remove racy clear_freeze_flag() and set PF_NOFREEZE on dead tasks
  freezer: rename thaw_process() to __thaw_task() and simplify the implementation
  ...
parents bb58dd5d 24b7ead3

Documentation/power/freezing-of-tasks.txt

+7 −7
Original line number Diff line number Diff line
@@ -21,7 +21,7 @@ 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

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
@@ -29,10 +29,10 @@ 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.



It is not recommended to call refrigerator() directly.  Instead, it is

recommended to 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.

__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.



For user space processes try_to_freeze() is called automatically from the

signal-handling code, but the freezable kernel threads need to call it
@@ -61,13 +61,13 @@ wait_event_freezable() and wait_event_freezable_timeout() macros. 
After the system memory state has been restored from a hibernation image and

devices have been reinitialized, the function thaw_processes() is called in

order to clear the PF_FROZEN flag for each frozen task.  Then, the tasks that

have been frozen leave refrigerator() and continue running.

have been frozen leave __refrigerator() and continue running.



III. Which kernel threads are freezable?



Kernel threads are not freezable by default.  However, a kernel thread may clear

PF_NOFREEZE for itself by calling set_freezable() (the resetting of PF_NOFREEZE

directly is strongly discouraged).  From this point it is regarded as freezable

directly is not allowed).  From this point it is regarded as freezable

and must call try_to_freeze() in a suitable place.



IV. Why do we do that?

arch/alpha/include/asm/thread_info.h

+0 −2
Original line number Diff line number Diff line
@@ -79,7 +79,6 @@ register struct thread_info *__current_thread_info __asm__("$8"); 
#define TIF_UAC_SIGBUS		12	/* ! userspace part of 'osf_sysinfo' */

#define TIF_MEMDIE		13	/* is terminating due to OOM killer */

#define TIF_RESTORE_SIGMASK	14	/* restore signal mask in do_signal */

#define TIF_FREEZE		16	/* is freezing for suspend */



#define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)

#define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)
@@ -87,7 +86,6 @@ register struct thread_info *__current_thread_info __asm__("$8"); 
#define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)

#define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)

#define _TIF_NOTIFY_RESUME	(1<<TIF_NOTIFY_RESUME)

#define _TIF_FREEZE		(1<<TIF_FREEZE)



/* Work to do on interrupt/exception return.  */

#define _TIF_WORK_MASK		(_TIF_SIGPENDING | _TIF_NEED_RESCHED | \

arch/arm/include/asm/thread_info.h

+0 −2
Original line number Diff line number Diff line
@@ -142,7 +142,6 @@ extern void vfp_flush_hwstate(struct thread_info *); 
#define TIF_POLLING_NRFLAG	16

#define TIF_USING_IWMMXT	17

#define TIF_MEMDIE		18	/* is terminating due to OOM killer */

#define TIF_FREEZE		19

#define TIF_RESTORE_SIGMASK	20

#define TIF_SECCOMP		21
@@ -152,7 +151,6 @@ extern void vfp_flush_hwstate(struct thread_info *); 
#define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)

#define _TIF_POLLING_NRFLAG	(1 << TIF_POLLING_NRFLAG)

#define _TIF_USING_IWMMXT	(1 << TIF_USING_IWMMXT)

#define _TIF_FREEZE		(1 << TIF_FREEZE)

#define _TIF_RESTORE_SIGMASK	(1 << TIF_RESTORE_SIGMASK)

#define _TIF_SECCOMP		(1 << TIF_SECCOMP)

arch/avr32/include/asm/thread_info.h

+0 −2
Original line number Diff line number Diff line
@@ -85,7 +85,6 @@ static inline struct thread_info *current_thread_info(void) 
#define TIF_RESTORE_SIGMASK	7	/* restore signal mask in do_signal */

#define TIF_CPU_GOING_TO_SLEEP	8	/* CPU is entering sleep 0 mode */

#define TIF_NOTIFY_RESUME	9	/* callback before returning to user */

#define TIF_FREEZE		29

#define TIF_DEBUG		30	/* debugging enabled */

#define TIF_USERSPACE		31      /* true if FS sets userspace */
@@ -98,7 +97,6 @@ static inline struct thread_info *current_thread_info(void) 
#define _TIF_RESTORE_SIGMASK	(1 << TIF_RESTORE_SIGMASK)

#define _TIF_CPU_GOING_TO_SLEEP (1 << TIF_CPU_GOING_TO_SLEEP)

#define _TIF_NOTIFY_RESUME	(1 << TIF_NOTIFY_RESUME)

#define _TIF_FREEZE		(1 << TIF_FREEZE)



/* Note: The masks below must never span more than 16 bits! */

arch/blackfin/include/asm/thread_info.h

+0 −2
Original line number Diff line number Diff line
@@ -100,7 +100,6 @@ static inline struct thread_info *current_thread_info(void) 
					   TIF_NEED_RESCHED */

#define TIF_MEMDIE		4	/* is terminating due to OOM killer */

#define TIF_RESTORE_SIGMASK	5	/* restore signal mask in do_signal() */

#define TIF_FREEZE		6	/* is freezing for suspend */

#define TIF_IRQ_SYNC		7	/* sync pipeline stage */

#define TIF_NOTIFY_RESUME	8	/* callback before returning to user */

#define TIF_SINGLESTEP		9
@@ -111,7 +110,6 @@ static inline struct thread_info *current_thread_info(void) 
#define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)

#define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)

#define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)

#define _TIF_FREEZE		(1<<TIF_FREEZE)

#define _TIF_IRQ_SYNC		(1<<TIF_IRQ_SYNC)

#define _TIF_NOTIFY_RESUME	(1<<TIF_NOTIFY_RESUME)

#define _TIF_SINGLESTEP		(1<<TIF_SINGLESTEP)