APM emulation: Notify about all suspend events, not just APM invoked ones (v2)

This revamps the apm-emulation code to get suspend notifications
regardless of what way pm_suspend() was invoked, whether via the
apm ioctl or via /sys/power/state. Also do some code cleanup and
add comments while at it.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Len Brown <len.brown@intel.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>

1 files changed, 207 insertions, 139 deletions

diff --git a/drivers/char/apm-emulation.c b/drivers/char/apm-emulation.c
index da8a1658a273..aaca40283be9 100644
--- a/drivers/char/apm-emulation.c
+++ b/drivers/char/apm-emulation.c
@@ -59,6 +59,55 @@ struct apm_queue {
 };
 
 /*
+ * thread states (for threads using a writable /dev/apm_bios fd):
+ *
+ * SUSPEND_NONE:        nothing happening
+ * SUSPEND_PENDING:     suspend event queued for thread and pending to be read
+ * SUSPEND_READ:        suspend event read, pending acknowledgement
+ * SUSPEND_ACKED:       acknowledgement received from thread (via ioctl),
+ *                      waiting for resume
+ * SUSPEND_ACKTO:       acknowledgement timeout
+ * SUSPEND_DONE:        thread had acked suspend and is now notified of
+ *                      resume
+ *
+ * SUSPEND_WAIT:        this thread invoked suspend and is waiting for resume
+ *
+ * A thread migrates in one of three paths:
+ *      NONE -1-> PENDING -2-> READ -3-> ACKED -4-> DONE -5-> NONE
+ *                                  -6-> ACKTO -7-> NONE
+ *      NONE -8-> WAIT -9-> NONE
+ *
+ * While in PENDING or READ, the thread is accounted for in the
+ * suspend_acks_pending counter.
+ *
+ * The transitions are invoked as follows:
+ *      1: suspend event is signalled from the core PM code
+ *      2: the suspend event is read from the fd by the userspace thread
+ *      3: userspace thread issues the APM_IOC_SUSPEND ioctl (as ack)
+ *      4: core PM code signals that we have resumed
+ *      5: APM_IOC_SUSPEND ioctl returns
+ *
+ *      6: the notifier invoked from the core PM code timed out waiting
+ *         for all relevant threds to enter ACKED state and puts those
+ *         that haven't into ACKTO
+ *      7: those threads issue APM_IOC_SUSPEND ioctl too late,
+ *         get an error
+ *
+ *      8: userspace thread issues the APM_IOC_SUSPEND ioctl (to suspend),
+ *         ioctl code invokes pm_suspend()
+ *      9: pm_suspend() returns indicating resume
+ */
+enum apm_suspend_state {
+        SUSPEND_NONE,
+        SUSPEND_PENDING,
+        SUSPEND_READ,
+        SUSPEND_ACKED,
+        SUSPEND_ACKTO,
+        SUSPEND_WAIT,
+        SUSPEND_DONE,
+};
+
+/*
  * The per-file APM data
  */
 struct apm_user {
@@ -69,13 +118,7 @@ struct apm_user {
         unsigned int            reader: 1;
 
         int                     suspend_result;
-        unsigned int            suspend_state;
-#define SUSPEND_NONE    0               /* no suspend pending */
-#define SUSPEND_PENDING 1               /* suspend pending read */
-#define SUSPEND_READ    2               /* suspend read, pending ack */
-#define SUSPEND_ACKED   3               /* suspend acked */
-#define SUSPEND_WAIT    4               /* waiting for suspend */
-#define SUSPEND_DONE    5               /* suspend completed */
+        enum apm_suspend_state  suspend_state;
 
         struct apm_queue        queue;
 };
@@ -83,7 +126,8 @@ struct apm_user {
 /*
  * Local variables
  */
-static int suspends_pending;
+static atomic_t suspend_acks_pending = ATOMIC_INIT(0);
+static atomic_t userspace_notification_inhibit = ATOMIC_INIT(0);
 static int apm_disabled;
 static struct task_struct *kapmd_tsk;
 
@@ -166,78 +210,6 @@ static void queue_event(apm_event_t event)
         wake_up_interruptible(&apm_waitqueue);
 }
 
-/*
- * queue_suspend_event - queue an APM suspend event.
- *
- * Check that we're in a state where we can suspend.  If not,
- * return -EBUSY.  Otherwise, queue an event to all "writer"
- * users.  If there are no "writer" users, return '1' to
- * indicate that we can immediately suspend.
- */
-static int queue_suspend_event(apm_event_t event, struct apm_user *sender)
-{
-        struct apm_user *as;
-        int ret = 1;
-
-        mutex_lock(&state_lock);
-        down_read(&user_list_lock);
-
-        /*
-         * If a thread is still processing, we can't suspend, so reject
-         * the request.
-         */
-        list_for_each_entry(as, &apm_user_list, list) {
-                if (as != sender && as->reader && as->writer && as->suser &&
-                    as->suspend_state != SUSPEND_NONE) {
-                        ret = -EBUSY;
-                        goto out;
-                }
-        }
-
-        list_for_each_entry(as, &apm_user_list, list) {
-                if (as != sender && as->reader && as->writer && as->suser) {
-                        as->suspend_state = SUSPEND_PENDING;
-                        suspends_pending++;
-                        queue_add_event(&as->queue, event);
-                        ret = 0;
-                }
-        }
- out:
-        up_read(&user_list_lock);
-        mutex_unlock(&state_lock);
-        wake_up_interruptible(&apm_waitqueue);
-        return ret;
-}
-
-static void apm_suspend(void)
-{
-        struct apm_user *as;
-        int err = pm_suspend(PM_SUSPEND_MEM);
-
-        /*
-         * Anyone on the APM queues will think we're still suspended.
-         * Send a message so everyone knows we're now awake again.
-         */
-        queue_event(APM_NORMAL_RESUME);
-
-        /*
-         * Finally, wake up anyone who is sleeping on the suspend.
-         */
-        mutex_lock(&state_lock);
-        down_read(&user_list_lock);
-        list_for_each_entry(as, &apm_user_list, list) {
-                if (as->suspend_state == SUSPEND_WAIT ||
-                    as->suspend_state == SUSPEND_ACKED) {
-                        as->suspend_result = err;
-                        as->suspend_state = SUSPEND_DONE;
-                }
-        }
-        up_read(&user_list_lock);
-        mutex_unlock(&state_lock);
-
-        wake_up(&apm_suspend_waitqueue);
-}
-
 static ssize_t apm_read(struct file *fp, char __user *buf, size_t count, loff_t *ppos)
 {
         struct apm_user *as = fp->private_data;
@@ -308,25 +280,22 @@ apm_ioctl(struct inode * inode, struct file *filp, u_int cmd, u_long arg)
 
                 as->suspend_result = -EINTR;
 
-                if (as->suspend_state == SUSPEND_READ) {
-                        int pending;
-
+                switch (as->suspend_state) {
+                case SUSPEND_READ:
                         /*
                          * If we read a suspend command from /dev/apm_bios,
                          * then the corresponding APM_IOC_SUSPEND ioctl is
                          * interpreted as an acknowledge.
                          */
                         as->suspend_state = SUSPEND_ACKED;
-                        suspends_pending--;
-                        pending = suspends_pending == 0;
+                        atomic_dec(&suspend_acks_pending);
                         mutex_unlock(&state_lock);
 
                         /*
-                         * If there are no further acknowledges required,
-                         * suspend the system.
+                         * suspend_acks_pending changed, the notifier needs to
+                         * be woken up for this
                          */
-                        if (pending)
-                                apm_suspend();
+                        wake_up(&apm_suspend_waitqueue);
 
                         /*
                          * Wait for the suspend/resume to complete.  If there
@@ -342,35 +311,21 @@ apm_ioctl(struct inode * inode, struct file *filp, u_int cmd, u_long arg)
                          * try_to_freeze() in freezer_count() will not trigger
                          */
                         freezer_count();
-                } else {
+                        break;
+                case SUSPEND_ACKTO:
+                        as->suspend_result = -ETIMEDOUT;
+                        mutex_unlock(&state_lock);
+                        break;
+                default:
                         as->suspend_state = SUSPEND_WAIT;
                         mutex_unlock(&state_lock);
 
                         /*
                          * Otherwise it is a request to suspend the system.
-                         * Queue an event for all readers, and expect an
-                         * acknowledge from all writers who haven't already
-                         * acknowledged.
-                         */
-                        err = queue_suspend_event(APM_USER_SUSPEND, as);
-                        if (err < 0) {
-                                /*
-                                 * Avoid taking the lock here - this
-                                 * should be fine.
-                                 */
-                                as->suspend_state = SUSPEND_NONE;
-                                break;
-                        }
-
-                        if (err > 0)
-                                apm_suspend();
-
-                        /*
-                         * Wait for the suspend/resume to complete.  If there
-                         * are pending acknowledges, we wait here for them.
+                         * Just invoke pm_suspend(), we'll handle it from
+                         * there via the notifier.
                          */
-                        wait_event_freezable(apm_suspend_waitqueue,
-                                         as->suspend_state == SUSPEND_DONE);
+                        as->suspend_result = pm_suspend(PM_SUSPEND_MEM);
                 }
 
                 mutex_lock(&state_lock);
@@ -386,7 +341,6 @@ apm_ioctl(struct inode * inode, struct file *filp, u_int cmd, u_long arg)
 static int apm_release(struct inode * inode, struct file * filp)
 {
         struct apm_user *as = filp->private_data;
-        int pending = 0;
 
         filp->private_data = NULL;
 
@@ -396,18 +350,15 @@ static int apm_release(struct inode * inode, struct file * filp)
 
         /*
          * We are now unhooked from the chain.  As far as new
-         * events are concerned, we no longer exist.  However, we
-         * need to balance suspends_pending, which means the
-         * possibility of sleeping.
+         * events are concerned, we no longer exist.
          */
         mutex_lock(&state_lock);
-        if (as->suspend_state != SUSPEND_NONE) {
-                suspends_pending -= 1;
-                pending = suspends_pending == 0;
-        }
+        if (as->suspend_state == SUSPEND_PENDING ||
+            as->suspend_state == SUSPEND_READ)
+                atomic_dec(&suspend_acks_pending);
         mutex_unlock(&state_lock);
-        if (pending)
-                apm_suspend();
+
+        wake_up(&apm_suspend_waitqueue);
 
         kfree(as);
         return 0;
@@ -545,7 +496,6 @@ static int kapmd(void *arg)
 {
         do {
                 apm_event_t event;
-                int ret;
 
                 wait_event_interruptible(kapmd_wait,
                                 !queue_empty(&kapmd_queue) || kthread_should_stop());
@@ -570,20 +520,13 @@ static int kapmd(void *arg)
 
                 case APM_USER_SUSPEND:
                 case APM_SYS_SUSPEND:
-                        ret = queue_suspend_event(event, NULL);
-                        if (ret < 0) {
-                                /*
-                                 * We were busy.  Try again in 50ms.
-                                 */
-                                queue_add_event(&kapmd_queue, event);
-                                msleep(50);
-                        }
-                        if (ret > 0)
-                                apm_suspend();
+                        pm_suspend(PM_SUSPEND_MEM);
                         break;
 
                 case APM_CRITICAL_SUSPEND:
-                        apm_suspend();
+                        atomic_inc(&userspace_notification_inhibit);
+                        pm_suspend(PM_SUSPEND_MEM);
+                        atomic_dec(&userspace_notification_inhibit);
                         break;
                 }
         } while (1);
@@ -591,6 +534,120 @@ static int kapmd(void *arg)
         return 0;
 }
 
+static int apm_suspend_notifier(struct notifier_block *nb,
+                                unsigned long event,
+                                void *dummy)
+{
+        struct apm_user *as;
+        int err;
+
+        /* short-cut emergency suspends */
+        if (atomic_read(&userspace_notification_inhibit))
+                return NOTIFY_DONE;
+
+        switch (event) {
+        case PM_SUSPEND_PREPARE:
+                /*
+                 * Queue an event to all "writer" users that we want
+                 * to suspend and need their ack.
+                 */
+                mutex_lock(&state_lock);
+                down_read(&user_list_lock);
+
+                list_for_each_entry(as, &apm_user_list, list) {
+                        if (as->suspend_state != SUSPEND_WAIT && as->reader &&
+                            as->writer && as->suser) {
+                                as->suspend_state = SUSPEND_PENDING;
+                                atomic_inc(&suspend_acks_pending);
+                                queue_add_event(&as->queue, APM_USER_SUSPEND);
+                        }
+                }
+
+                up_read(&user_list_lock);
+                mutex_unlock(&state_lock);
+                wake_up_interruptible(&apm_waitqueue);
+
+                /*
+                 * Wait for the the suspend_acks_pending variable to drop to
+                 * zero, meaning everybody acked the suspend event (or the
+                 * process was killed.)
+                 *
+                 * If the app won't answer within a short while we assume it
+                 * locked up and ignore it.
+                 */
+                err = wait_event_interruptible_timeout(
+                        apm_suspend_waitqueue,
+                        atomic_read(&suspend_acks_pending) == 0,
+                        5*HZ);
+
+                /* timed out */
+                if (err == 0) {
+                        /*
+                         * Move anybody who timed out to "ack timeout" state.
+                         *
+                         * We could time out and the userspace does the ACK
+                         * right after we time out but before we enter the
+                         * locked section here, but that's fine.
+                         */
+                        mutex_lock(&state_lock);
+                        down_read(&user_list_lock);
+                        list_for_each_entry(as, &apm_user_list, list) {
+                                if (as->suspend_state == SUSPEND_PENDING ||
+                                    as->suspend_state == SUSPEND_READ) {
+                                        as->suspend_state = SUSPEND_ACKTO;
+                                        atomic_dec(&suspend_acks_pending);
+                                }
+                        }
+                        up_read(&user_list_lock);
+                        mutex_unlock(&state_lock);
+                }
+
+                /* let suspend proceed */
+                if (err >= 0)
+                        return NOTIFY_OK;
+
+                /* interrupted by signal */
+                return NOTIFY_BAD;
+
+        case PM_POST_SUSPEND:
+                /*
+                 * Anyone on the APM queues will think we're still suspended.
+                 * Send a message so everyone knows we're now awake again.
+                 */
+                queue_event(APM_NORMAL_RESUME);
+
+                /*
+                 * Finally, wake up anyone who is sleeping on the suspend.
+                 */
+                mutex_lock(&state_lock);
+                down_read(&user_list_lock);
+                list_for_each_entry(as, &apm_user_list, list) {
+                        if (as->suspend_state == SUSPEND_ACKED) {
+                                /*
+                                 * TODO: maybe grab error code, needs core
+                                 * changes to push the error to the notifier
+                                 * chain (could use the second parameter if
+                                 * implemented)
+                                 */
+                                as->suspend_result = 0;
+                                as->suspend_state = SUSPEND_DONE;
+                        }
+                }
+                up_read(&user_list_lock);
+                mutex_unlock(&state_lock);
+
+                wake_up(&apm_suspend_waitqueue);
+                return NOTIFY_OK;
+
+        default:
+                return NOTIFY_DONE;
+        }
+}
+
+static struct notifier_block apm_notif_block = {
+        .notifier_call = apm_suspend_notifier,
+};
+
 static int __init apm_init(void)
 {
         int ret;
@@ -604,7 +661,7 @@ static int __init apm_init(void)
         if (IS_ERR(kapmd_tsk)) {
                 ret = PTR_ERR(kapmd_tsk);
                 kapmd_tsk = NULL;
-                return ret;
+                goto out;
         }
         wake_up_process(kapmd_tsk);
 
@@ -613,16 +670,27 @@ static int __init apm_init(void)
 #endif
 
         ret = misc_register(&apm_device);
-        if (ret != 0) {
-                remove_proc_entry("apm", NULL);
-                kthread_stop(kapmd_tsk);
-        }
+        if (ret)
+                goto out_stop;
 
+        ret = register_pm_notifier(&apm_notif_block);
+        if (ret)
+                goto out_unregister;
+
+        return 0;
+
+ out_unregister:
+        misc_deregister(&apm_device);
+ out_stop:
+        remove_proc_entry("apm", NULL);
+        kthread_stop(kapmd_tsk);
+ out:
         return ret;
 }
 
 static void __exit apm_exit(void)
 {
+        unregister_pm_notifier(&apm_notif_block);
         misc_deregister(&apm_device);
         remove_proc_entry("apm", NULL);