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Subject[PATCH] PM / Hibernate: Fix s2disk regression related to unlock_system_sleep()
Date
From: Rafael J. Wysocki <rjw@sisk.pl>

Commit bcda53faf5814c0c6025a0bd47108adfcbe9f199, "PM / Sleep: Replace
mutex_[un]lock(&pm_mutex) with [un]lock_system_sleep()", modified
snapshot_read() and snapshot_write() in kernel/power/user.c, among
other things, by making them use lock_system_sleep() and
unlock_system_sleep() instead of just locking and unlocking pm_mutex.
Unfortunately, however, this was a mistake, because these routines
are supposed to be executed after processes have been frozen
(i.e. when system_freezing_cnt is nonzero), so when
unlock_system_sleep() is executed by one of them, this causes the
caller to execute try_to_freeze() and go into the refrigerator as
a result. This, in turn, deadlocks the suspend process and locks up
the system.

Fix the problem by reverting the part of commit bcda53faf5814c0c6025a
that changed snapshot_read() and snapshot_write(). Additionally,
make these functions check system_freezing_cnt and return error codes
if it is zero to ensure that they won't do anything if tasks have not
been frozen.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
---
kernel/power/user.c | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)
Index: linux/kernel/power/user.c
===================================================================
--- linux.orig/kernel/power/user.c
+++ linux/kernel/power/user.c
@@ -137,7 +137,10 @@ static ssize_t snapshot_read(struct file
ssize_t res;
loff_t pg_offp = *offp & ~PAGE_MASK;

- lock_system_sleep();
+ if (!atomic_read(&system_freezing_cnt))
+ return -EBUSY;
+
+ mutex_lock(&pm_mutex);

data = filp->private_data;
if (!data->ready) {
@@ -158,7 +161,7 @@ static ssize_t snapshot_read(struct file
*offp += res;

Unlock:
- unlock_system_sleep();
+ mutex_unlock(&pm_mutex);

return res;
}
@@ -170,7 +173,10 @@ static ssize_t snapshot_write(struct fil
ssize_t res;
loff_t pg_offp = *offp & ~PAGE_MASK;

- lock_system_sleep();
+ if (!atomic_read(&system_freezing_cnt))
+ return -EBUSY;
+
+ mutex_lock(&pm_mutex);

data = filp->private_data;

@@ -187,7 +193,7 @@ static ssize_t snapshot_write(struct fil
if (res > 0)
*offp += res;
unlock:
- unlock_system_sleep();
+ mutex_unlock(&pm_mutex);

return res;
}

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