[PATCH v2 4/4] PM: hibernate: don't set PF_FREEZER_SKIP flag when manipulating /dev/snapshot

[Tetsuo Handa]

Since khungtaskd skips threads with PF_FREEZER_SKIP flag set, currently
we can't report unbounded uninterruptible sleep when something went wrong
while manipulating /dev/snapshot interface.

Let's change snapshot_{open,read,write}() to use mutex_lock_killable()
and change snapshot_release() to use mutex_lock(), so that khungtaskd can
report unbounded uninterruptible sleep, by not setting PF_FREEZER_SKIP
flag.

Since /dev/snapshot is exclusive due to hibernate_acquire(), we could
choose mutex_trylock() for snapshot_{open,read,write}() as with
snapshot_ioctl(). But until we confirm that this patch does not
break something, let's stay mutex_lock_killable().

Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
Cc: Len Brown <len.brown@xxxxxxxxx>
Cc: Pavel Machek <pavel@xxxxxx>
---
This patch is only compile tested. Need to review if somewhere depends
on PF_FREEZER_SKIP flag being set.

 kernel/power/user.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/kernel/power/user.c b/kernel/power/user.c
index 32dd5a855e8c..9936efa07022 100644
--- a/kernel/power/user.c
+++ b/kernel/power/user.c
@@ -68,7 +68,8 @@ static int snapshot_open(struct inode *inode, struct file *filp)
 		break;
 	}
 
-	lock_system_sleep();
+	if (mutex_lock_killable(&system_transition_mutex))
+		return -EINTR;
 
 	if (!hibernate_acquire()) {
 		error = -EBUSY;
@@ -102,7 +103,7 @@ static int snapshot_open(struct inode *inode, struct file *filp)
 	data->dev = 0;
 
  Unlock:
-	unlock_system_sleep();
+	mutex_unlock(&system_transition_mutex);
 
 	return error;
 }
@@ -111,7 +112,7 @@ static int snapshot_release(struct inode *inode, struct file *filp)
 {
 	struct snapshot_data *data;
 
-	lock_system_sleep();
+	mutex_lock(&system_transition_mutex);
 
 	swsusp_free();
 	data = filp->private_data;
@@ -128,7 +129,7 @@ static int snapshot_release(struct inode *inode, struct file *filp)
 			PM_POST_HIBERNATION : PM_POST_RESTORE);
 	hibernate_release();
 
-	unlock_system_sleep();
+	mutex_unlock(&system_transition_mutex);
 
 	return 0;
 }
@@ -140,7 +141,8 @@ static ssize_t snapshot_read(struct file *filp, char __user *buf,
 	ssize_t res;
 	loff_t pg_offp = *offp & ~PAGE_MASK;
 
-	lock_system_sleep();
+	if (mutex_lock_killable(&system_transition_mutex))
+		return -EINTR;
 
 	data = filp->private_data;
 	if (!data->ready) {
@@ -161,7 +163,7 @@ static ssize_t snapshot_read(struct file *filp, char __user *buf,
 		*offp += res;
 
  Unlock:
-	unlock_system_sleep();
+	mutex_unlock(&system_transition_mutex);
 
 	return res;
 }
@@ -173,7 +175,8 @@ static ssize_t snapshot_write(struct file *filp, const char __user *buf,
 	ssize_t res;
 	loff_t pg_offp = *offp & ~PAGE_MASK;
 
-	lock_system_sleep();
+	if (mutex_lock_killable(&system_transition_mutex))
+		return -EINTR;
 
 	data = filp->private_data;
 
@@ -195,7 +198,7 @@ static ssize_t snapshot_write(struct file *filp, const char __user *buf,
 	if (res > 0)
 		*offp += res;
 unlock:
-	unlock_system_sleep();
+	mutex_unlock(&system_transition_mutex);
 
 	return res;
 }
-- 
2.18.4