freezer: clean up freeze_processes() failure path

freeze_processes() failure path is rather messy.  Freezing is canceled
for workqueues and tasks which aren't frozen yet but frozen tasks are
left alone and should be thawed by the caller and of course some
callers (xen and kexec) didn't do it.

This patch updates __thaw_task() to handle cancelation correctly and
makes freeze_processes() and freeze_kernel_threads() call
thaw_processes() on failure instead so that the system is fully thawed
on failure.  Unnecessary [suspend_]thaw_processes() calls are removed
from kernel/power/hibernate.c, suspend.c and user.c.

While at it, restructure error checking if clause in suspend_prepare()
to be less weird.

-v2: Srivatsa spotted missing removal of suspend_thaw_processes() in
     suspend_prepare() and error in commit message.  Updated.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>

5 files changed, 23 insertions, 45 deletions

diff --git a/kernel/freezer.c b/kernel/freezer.c
index b8b562124ba9..11e32d419dec 100644
--- a/kernel/freezer.c
+++ b/kernel/freezer.c
@@ -129,21 +129,6 @@ out_unlock:
 	return ret;
 }
 
-void cancel_freezing(struct task_struct *p)
-{
-	unsigned long flags;
-
-	spin_lock_irqsave(&freezer_lock, flags);
-	if (freezing(p)) {
-		pr_debug("  clean up: %s\n", p->comm);
-		clear_freeze_flag(p);
-		spin_lock(&p->sighand->siglock);
-		recalc_sigpending_and_wake(p);
-		spin_unlock(&p->sighand->siglock);
-	}
-	spin_unlock_irqrestore(&freezer_lock, flags);
-}
-
 void __thaw_task(struct task_struct *p)
 {
 	unsigned long flags;
@@ -153,10 +138,18 @@ void __thaw_task(struct task_struct *p)
 	 * be visible to @p as waking up implies wmb.  Waking up inside
 	 * freezer_lock also prevents wakeups from leaking outside
 	 * refrigerator.
+	 *
+	 * If !FROZEN, @p hasn't reached refrigerator, recalc sigpending to
+	 * avoid leaving dangling TIF_SIGPENDING behind.
 	 */
 	spin_lock_irqsave(&freezer_lock, flags);
 	clear_freeze_flag(p);
-	if (frozen(p))
+	if (frozen(p)) {
 		wake_up_process(p);
+	} else {
+		spin_lock(&p->sighand->siglock);
+		recalc_sigpending_and_wake(p);
+		spin_unlock(&p->sighand->siglock);
+	}
 	spin_unlock_irqrestore(&freezer_lock, flags);
 }
diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
index 196c01268ebd..ba2319ffc860 100644
--- a/kernel/power/hibernate.c
+++ b/kernel/power/hibernate.c
@@ -607,17 +607,6 @@ static void power_down(void)
 	while(1);
 }
 
-static int prepare_processes(void)
-{
-	int error = 0;
-
-	if (freeze_processes()) {
-		error = -EBUSY;
-		thaw_processes();
-	}
-	return error;
-}
-
 /**
  * hibernate - Carry out system hibernation, including saving the image.
  */
@@ -650,7 +639,7 @@ int hibernate(void)
 	sys_sync();
 	printk("done.\n");
 
-	error = prepare_processes();
+	error = freeze_processes();
 	if (error)
 		goto Finish;
 
@@ -811,7 +800,7 @@ static int software_resume(void)
 		goto close_finish;
 
 	pr_debug("PM: Preparing processes for restore.\n");
-	error = prepare_processes();
+	error = freeze_processes();
 	if (error) {
 		swsusp_close(FMODE_READ);
 		goto Done;
diff --git a/kernel/power/process.c b/kernel/power/process.c
index e59676f5811d..ce643838a00c 100644
--- a/kernel/power/process.c
+++ b/kernel/power/process.c
@@ -91,11 +91,6 @@ static int try_to_freeze_tasks(bool sig_only)
 	elapsed_csecs = elapsed_csecs64;
 
 	if (todo) {
-		/* This does not unfreeze processes that are already frozen
-		 * (we have slightly ugly calling convention in that respect,
-		 * and caller must call thaw_processes() if something fails),
-		 * but it cleans up leftover PF_FREEZE requests.
-		 */
 		printk("\n");
 		printk(KERN_ERR "Freezing of tasks %s after %d.%02d seconds "
 		       "(%d tasks refusing to freeze, wq_busy=%d):\n",
@@ -103,14 +98,11 @@ static int try_to_freeze_tasks(bool sig_only)
 		       elapsed_csecs / 100, elapsed_csecs % 100,
 		       todo - wq_busy, wq_busy);
 
-		thaw_workqueues();
-
 		read_lock(&tasklist_lock);
 		do_each_thread(g, p) {
 			if (!wakeup && !freezer_should_skip(p) &&
 			    freezing(p) && !frozen(p))
 				sched_show_task(p);
-			cancel_freezing(p);
 		} while_each_thread(g, p);
 		read_unlock(&tasklist_lock);
 	} else {
@@ -123,6 +115,8 @@ static int try_to_freeze_tasks(bool sig_only)
 
 /**
  * freeze_processes - Signal user space processes to enter the refrigerator.
+ *
+ * On success, returns 0.  On failure, -errno and system is fully thawed.
  */
 int freeze_processes(void)
 {
@@ -137,11 +131,15 @@ int freeze_processes(void)
 	printk("\n");
 	BUG_ON(in_atomic());
 
+	if (error)
+		thaw_processes();
 	return error;
 }
 
 /**
  * freeze_kernel_threads - Make freezable kernel threads go to the refrigerator.
+ *
+ * On success, returns 0.  On failure, -errno and system is fully thawed.
  */
 int freeze_kernel_threads(void)
 {
@@ -155,6 +153,8 @@ int freeze_kernel_threads(void)
 	printk("\n");
 	BUG_ON(in_atomic());
 
+	if (error)
+		thaw_processes();
 	return error;
 }
 
diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
index 4953dc054c53..d336b27d1104 100644
--- a/kernel/power/suspend.c
+++ b/kernel/power/suspend.c
@@ -106,13 +106,11 @@ static int suspend_prepare(void)
 		goto Finish;
 
 	error = suspend_freeze_processes();
-	if (error) {
-		suspend_stats.failed_freeze++;
-		dpm_save_failed_step(SUSPEND_FREEZE);
-	} else
+	if (!error)
 		return 0;
 
-	suspend_thaw_processes();
+	suspend_stats.failed_freeze++;
+	dpm_save_failed_step(SUSPEND_FREEZE);
 	usermodehelper_enable();
  Finish:
 	pm_notifier_call_chain(PM_POST_SUSPEND);
diff --git a/kernel/power/user.c b/kernel/power/user.c
index 6d8f535c2b88..7cc3f5bc5c24 100644
--- a/kernel/power/user.c
+++ b/kernel/power/user.c
@@ -257,10 +257,8 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd,
 			break;
 
 		error = freeze_processes();
-		if (error) {
-			thaw_processes();
+		if (error)
 			usermodehelper_enable();
-		}
 		if (!error)
 			data->frozen = 1;
 		break;