apm-emulation: apm_mutex breaks ACK; remove it

apm_mutex is locked by a process (e.g. apm -s) at the start of apm_ioctl() and
remains locked while pm_suspend() is called. Any subsequent process trying to
ACK the suspend (e.g. apmd) is then blocked at the start of apm_ioctl(),
causing the suspend to be delayed for 5 seconds in apm_suspend_notifier()
while the ACK times out. In short, ACKs don't work.

The driver's data structures are sufficiently protected by assorted locks. And
pm_suspend() has its own mutex to prevent reentrancy. Consequently there is no
obvious requirement for apm_mutex, which evolved from earlier BKL calls. So
let's remove it.

Signed-off-by: Paul Parsons <lost.distance@yahoo.com>
Acked-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

diff --git a/drivers/char/apm-emulation.c b/drivers/char/apm-emulation.c
index 45b987c..548708c 100644 (file)
--- a/drivers/char/apm-emulation.c
+++ b/drivers/char/apm-emulation.c
@@ -126,7 +126,6 @@ struct apm_user {
 /*
  * Local variables
  */
-static DEFINE_MUTEX(apm_mutex);
 static atomic_t suspend_acks_pending = ATOMIC_INIT(0);
 static atomic_t userspace_notification_inhibit = ATOMIC_INIT(0);
 static int apm_disabled;
@@ -275,7 +274,6 @@ apm_ioctl(struct file *filp, u_int cmd, u_long arg)
        if (!as->suser || !as->writer)
                return -EPERM;
 
-       mutex_lock(&apm_mutex);
        switch (cmd) {
        case APM_IOC_SUSPEND:
                mutex_lock(&state_lock);
@@ -336,7 +334,6 @@ apm_ioctl(struct file *filp, u_int cmd, u_long arg)
                mutex_unlock(&state_lock);
                break;
        }
-       mutex_unlock(&apm_mutex);
 
        return err;
 }
@@ -371,7 +368,6 @@ static int apm_open(struct inode * inode, struct file * filp)
 {
        struct apm_user *as;
 
-       mutex_lock(&apm_mutex);
        as = kzalloc(sizeof(*as), GFP_KERNEL);
        if (as) {
                /*
@@ -391,7 +387,6 @@ static int apm_open(struct inode * inode, struct file * filp)
 
                filp->private_data = as;
        }
-       mutex_unlock(&apm_mutex);
 
        return as ? 0 : -ENOMEM;
 }