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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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