freezer: unexport refrigerator() and update try_to_freeze() slightly

There is no reason to export two functions for entering the
refrigerator.  Calling refrigerator() instead of try_to_freeze()
doesn't save anything noticeable or removes any race condition.

* Rename refrigerator() to __refrigerator() and make it return bool
  indicating whether it scheduled out for freezing.

* Update try_to_freeze() to return bool and relay the return value of
  __refrigerator() if freezing().

* Convert all refrigerator() users to try_to_freeze().

* Update documentation accordingly.

* While at it, add might_sleep() to try_to_freeze().

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Samuel Ortiz <samuel@sortiz.org>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Steven Whitehouse <swhiteho@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jan Kara <jack@suse.cz>
Cc: KONISHI Ryusuke <konishi.ryusuke@lab.ntt.co.jp>
Cc: Christoph Hellwig <hch@infradead.org>

Documentation/power/freezing-of-tasks.txt

@@ -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
@@ -61,7 +61,7 @@ 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?
 

drivers/net/irda/stir4200.c

@@ -750,7 +750,7 @@ static int stir_transmit_thread(void *arg)
 
 			write_reg(stir, REG_CTRL1, CTRL1_TXPWD|CTRL1_RXPWD);
 
-			refrigerator();
+			try_to_freeze();
 
 			if (change_speed(stir, stir->speed))
 				break;

fs/btrfs/async-thread.c

@@ -340,7 +340,7 @@ again:
 		if (freezing(current)) {
 			worker->working = 0;
 			spin_unlock_irq(&worker->lock);
-			refrigerator();
+			try_to_freeze();
 		} else {
 			spin_unlock_irq(&worker->lock);
 			if (!kthread_should_stop()) {

fs/btrfs/disk-io.c

@@ -1579,9 +1579,7 @@ static int cleaner_kthread(void *arg)
 			btrfs_run_defrag_inodes(root->fs_info);
 		}
 
-		if (freezing(current)) {
-			refrigerator();
-		} else {
+		if (!try_to_freeze()) {
 			set_current_state(TASK_INTERRUPTIBLE);
 			if (!kthread_should_stop())
 				schedule();
@@ -1635,9 +1633,7 @@ sleep:
 		wake_up_process(root->fs_info->cleaner_kthread);
 		mutex_unlock(&root->fs_info->transaction_kthread_mutex);
 
-		if (freezing(current)) {
-			refrigerator();
-		} else {
+		if (!try_to_freeze()) {
 			set_current_state(TASK_INTERRUPTIBLE);
 			if (!kthread_should_stop() &&
 			    !btrfs_transaction_blocked(root->fs_info))

fs/ext4/super.c

@@ -2882,8 +2882,7 @@ cont_thread:
 		}
 		mutex_unlock(&eli->li_list_mtx);
 
-		if (freezing(current))
-			refrigerator();
+		try_to_freeze();
 
 		cur = jiffies;
 		if ((time_after_eq(cur, next_wakeup)) ||

fs/gfs2/log.c

@@ -951,8 +951,8 @@ int gfs2_logd(void *data)
 			wake_up(&sdp->sd_log_waitq);
 
 		t = gfs2_tune_get(sdp, gt_logd_secs) * HZ;
-		if (freezing(current))
-			refrigerator();
+
+		try_to_freeze();
 
 		do {
 			prepare_to_wait(&sdp->sd_logd_waitq, &wait,

fs/gfs2/quota.c

@@ -1427,8 +1427,8 @@ int gfs2_quotad(void *data)
 		/* Check for & recover partially truncated inodes */
 		quotad_check_trunc_list(sdp);
 
-		if (freezing(current))
-			refrigerator();
+		try_to_freeze();
+
 		t = min(quotad_timeo, statfs_timeo);
 
 		prepare_to_wait(&sdp->sd_quota_wait, &wait, TASK_INTERRUPTIBLE);

fs/jbd/journal.c

@@ -166,7 +166,7 @@ loop:
 		 */
 		jbd_debug(1, "Now suspending kjournald\n");
 		spin_unlock(&journal->j_state_lock);
-		refrigerator();
+		try_to_freeze();
 		spin_lock(&journal->j_state_lock);
 	} else {
 		/*

fs/jbd2/journal.c

@@ -173,7 +173,7 @@ loop:
 		 */
 		jbd_debug(1, "Now suspending kjournald2\n");
 		write_unlock(&journal->j_state_lock);
-		refrigerator();
+		try_to_freeze();
 		write_lock(&journal->j_state_lock);
 	} else {
 		/*

fs/jfs/jfs_logmgr.c

@@ -2349,7 +2349,7 @@ int jfsIOWait(void *arg)
 
 		if (freezing(current)) {
 			spin_unlock_irq(&log_redrive_lock);
-			refrigerator();
+			try_to_freeze();
 		} else {
 			set_current_state(TASK_INTERRUPTIBLE);
 			spin_unlock_irq(&log_redrive_lock);

fs/jfs/jfs_txnmgr.c

@@ -2800,7 +2800,7 @@ int jfs_lazycommit(void *arg)
 
 		if (freezing(current)) {
 			LAZY_UNLOCK(flags);
-			refrigerator();
+			try_to_freeze();
 		} else {
 			DECLARE_WAITQUEUE(wq, current);
 
@@ -2994,7 +2994,7 @@ int jfs_sync(void *arg)
 
 		if (freezing(current)) {
 			TXN_UNLOCK();
-			refrigerator();
+			try_to_freeze();
 		} else {
 			set_current_state(TASK_INTERRUPTIBLE);
 			TXN_UNLOCK();

fs/nilfs2/segment.c

@@ -2470,7 +2470,7 @@ static int nilfs_segctor_thread(void *arg)
 
 	if (freezing(current)) {
 		spin_unlock(&sci->sc_state_lock);
-		refrigerator();
+		try_to_freeze();
 		spin_lock(&sci->sc_state_lock);
 	} else {
 		DEFINE_WAIT(wait);

fs/xfs/xfs_buf.c

@@ -1703,7 +1703,7 @@ xfsbufd(
 
 		if (unlikely(freezing(current))) {
 			set_bit(XBT_FORCE_SLEEP, &target->bt_flags);
-			refrigerator();
+			try_to_freeze();
 		} else {
 			clear_bit(XBT_FORCE_SLEEP, &target->bt_flags);
 		}

include/linux/freezer.h

@@ -47,18 +47,17 @@ static inline bool should_send_signal(struct task_struct *p)
 /* Takes and releases task alloc lock using task_lock() */
 extern int thaw_process(struct task_struct *p);
 
-extern void refrigerator(void);
+extern bool __refrigerator(void);
 extern int freeze_processes(void);
 extern int freeze_kernel_threads(void);
 extern void thaw_processes(void);
 
-static inline int try_to_freeze(void)
+static inline bool try_to_freeze(void)
 {
-	if (freezing(current)) {
-		refrigerator();
-		return 1;
-	} else
-		return 0;
+	might_sleep();
+	if (likely(!freezing(current)))
+		return false;
+	return __refrigerator();
 }
 
 extern bool freeze_task(struct task_struct *p, bool sig_only);
@@ -181,12 +180,12 @@ static inline void set_freeze_flag(struct task_struct *p) {}
 static inline void clear_freeze_flag(struct task_struct *p) {}
 static inline int thaw_process(struct task_struct *p) { return 1; }
 
-static inline void refrigerator(void) {}
+static inline bool __refrigerator(void) { return false; }
 static inline int freeze_processes(void) { return -ENOSYS; }
 static inline int freeze_kernel_threads(void) { return -ENOSYS; }
 static inline void thaw_processes(void) {}
 
-static inline int try_to_freeze(void) { return 0; }
+static inline bool try_to_freeze(void) { return false; }
 
 static inline void freezer_do_not_count(void) {}
 static inline void freezer_count(void) {}

kernel/freezer.c

@@ -23,10 +23,11 @@ static inline void frozen_process(void)
 }
 
 /* Refrigerator is place where frozen processes are stored :-). */
-void refrigerator(void)
+bool __refrigerator(void)
 {
 	/* Hmm, should we be allowed to suspend when there are realtime
 	   processes around? */
+	bool was_frozen = false;
 	long save;
 
 	task_lock(current);
@@ -35,7 +36,7 @@ void refrigerator(void)
 		task_unlock(current);
 	} else {
 		task_unlock(current);
-		return;
+		return was_frozen;
 	}
 	save = current->state;
 	pr_debug("%s entered refrigerator\n", current->comm);
@@ -51,6 +52,7 @@ void refrigerator(void)
 		set_current_state(TASK_UNINTERRUPTIBLE);
 		if (!frozen(current))
 			break;
+		was_frozen = true;
 		schedule();
 	}
 
@@ -65,8 +67,10 @@ void refrigerator(void)
 	 * synchronization which depends on ordered task state change.
 	 */
 	set_current_state(save);
+
+	return was_frozen;
 }
-EXPORT_SYMBOL(refrigerator);
+EXPORT_SYMBOL(__refrigerator);
 
 static void fake_signal_wake_up(struct task_struct *p)
 {