HID: picolcd: implement refcounting of framebuffer

As our device may be hot-unplugged and framebuffer cannot handle
this case by itself we need to keep track of usage count so as
to release fb_info and framebuffer memory only after the last user
has closed framebuffer.

We need to do the freeing in a scheduled work as fb_release()
is called with fb_info lock held.

Signed-off-by: Bruno Prémont <bonbons@linux-vserver.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

1 files changed, 103 insertions, 7 deletions

diff --git a/drivers/hid/hid-picolcd.c b/drivers/hid/hid-picolcd.c
index f7204541591c..346f0e34987e 100644
--- a/drivers/hid/hid-picolcd.c
+++ b/drivers/hid/hid-picolcd.c
@@ -439,6 +439,9 @@ static void picolcd_fb_update(struct picolcd_data *data)
         int chip, tile, n;
         unsigned long flags;
 
+        if (!data)
+                return;
+
         spin_lock_irqsave(&data->lock, flags);
         if (!(data->status & PICOLCD_READY_FB)) {
                 spin_unlock_irqrestore(&data->lock, flags);
@@ -461,6 +464,8 @@ static void picolcd_fb_update(struct picolcd_data *data)
                                         data->fb_bitmap, data->fb_bpp, chip, tile) ||
                                 data->fb_force) {
                                 n += 2;
+                                if (!data->fb_info->par)
+                                        return; /* device lost! */
                                 if (n >= HID_OUTPUT_FIFO_SIZE / 2) {
                                         usbhid_wait_io(data->hdev);
                                         n = 0;
@@ -531,11 +536,23 @@ static int picolcd_fb_blank(int blank, struct fb_info *info)
 static void picolcd_fb_destroy(struct fb_info *info)
 {
         struct picolcd_data *data = info->par;
+        u32 *ref_cnt = info->pseudo_palette;
+        int may_release;
+
         info->par = NULL;
         if (data)
                 data->fb_info = NULL;
         fb_deferred_io_cleanup(info);
-        framebuffer_release(info);
+
+        ref_cnt--;
+        mutex_lock(&info->lock);
+        (*ref_cnt)--;
+        may_release = !ref_cnt;
+        mutex_unlock(&info->lock);
+        if (may_release) {
+                framebuffer_release(info);
+                vfree((u8 *)info->fix.smem_start);
+        }
 }
 
 static int picolcd_fb_check_var(struct fb_var_screeninfo *var, struct fb_info *info)
@@ -564,6 +581,8 @@ static int picolcd_set_par(struct fb_info *info)
 {
         struct picolcd_data *data = info->par;
         u8 *tmp_fb, *o_fb;
+        if (!data)
+                return -ENODEV;
         if (info->var.bits_per_pixel == data->fb_bpp)
                 return 0;
         /* switch between 1/8 bit depths */
@@ -603,10 +622,77 @@ static int picolcd_set_par(struct fb_info *info)
         return 0;
 }
 
+/* Do refcounting on our FB and cleanup per worker if FB is
+ * closed after unplug of our device
+ * (fb_release holds info->lock and still touches info after
+ *  we return so we can't release it immediately.
+ */
+struct picolcd_fb_cleanup_item {
+        struct fb_info *info;
+        struct picolcd_fb_cleanup_item *next;
+};
+static struct picolcd_fb_cleanup_item *fb_pending;
+DEFINE_SPINLOCK(fb_pending_lock);
+
+static void picolcd_fb_do_cleanup(struct work_struct *data)
+{
+        struct picolcd_fb_cleanup_item *item;
+        unsigned long flags;
+
+        do {
+                spin_lock_irqsave(&fb_pending_lock, flags);
+                item = fb_pending;
+                fb_pending = item ? item->next : NULL;
+                spin_unlock_irqrestore(&fb_pending_lock, flags);
+
+                if (item) {
+                        u8 *fb = (u8 *)item->info->fix.smem_start;
+                        /* make sure we do not race against fb core when
+                         * releasing */
+                        mutex_lock(&item->info->lock);
+                        mutex_unlock(&item->info->lock);
+                        framebuffer_release(item->info);
+                        vfree(fb);
+                }
+        } while (item);
+}
+
+DECLARE_WORK(picolcd_fb_cleanup, picolcd_fb_do_cleanup);
+
+static int picolcd_fb_open(struct fb_info *info, int u)
+{
+        u32 *ref_cnt = info->pseudo_palette;
+        ref_cnt--;
+
+        (*ref_cnt)++;
+        return 0;
+}
+
+static int picolcd_fb_release(struct fb_info *info, int u)
+{
+        u32 *ref_cnt = info->pseudo_palette;
+        ref_cnt--;
+
+        (*ref_cnt)++;
+        if (!*ref_cnt) {
+                unsigned long flags;
+                struct picolcd_fb_cleanup_item *item = (struct picolcd_fb_cleanup_item *)ref_cnt;
+                item--;
+                spin_lock_irqsave(&fb_pending_lock, flags);
+                item->next = fb_pending;
+                fb_pending = item;
+                spin_unlock_irqrestore(&fb_pending_lock, flags);
+                schedule_work(&picolcd_fb_cleanup);
+        }
+        return 0;
+}
+
 /* Note this can't be const because of struct fb_info definition */
 static struct fb_ops picolcdfb_ops = {
         .owner        = THIS_MODULE,
         .fb_destroy   = picolcd_fb_destroy,
+        .fb_open      = picolcd_fb_open,
+        .fb_release   = picolcd_fb_release,
         .fb_read      = fb_sys_read,
         .fb_write     = picolcd_fb_write,
         .fb_blank     = picolcd_fb_blank,
@@ -708,13 +794,13 @@ static int picolcd_init_framebuffer(struct picolcd_data *data)
          * - u32 for ref_count
          * - 256*u32 for pseudo_palette
          */
-        info = framebuffer_alloc(257 * sizeof(u32), dev);
+        info = framebuffer_alloc(257 * sizeof(u32) + sizeof(struct picolcd_fb_cleanup_item), dev);
         if (info == NULL) {
                 dev_err(dev, "failed to allocate a framebuffer\n");
                 goto err_nomem;
         }
 
-        palette  = info->par;
+        palette  = info->par + sizeof(struct picolcd_fb_cleanup_item);
         *palette = 1;
         palette++;
         for (i = 0; i < 256; i++)
@@ -775,18 +861,17 @@ static void picolcd_exit_framebuffer(struct picolcd_data *data)
 {
         struct fb_info *info = data->fb_info;
         u8 *fb_vbitmap = data->fb_vbitmap;
-        u8 *fb_bitmap  = data->fb_bitmap;
 
         if (!info)
                 return;
 
+        info->par = NULL;
+        device_remove_file(&data->hdev->dev, &dev_attr_fb_update_rate);
+        unregister_framebuffer(info);
         data->fb_vbitmap = NULL;
         data->fb_bitmap  = NULL;
         data->fb_bpp     = 0;
         data->fb_info    = NULL;
-        device_remove_file(&data->hdev->dev, &dev_attr_fb_update_rate);
-        unregister_framebuffer(info);
-        vfree(fb_bitmap);
         kfree(fb_vbitmap);
 }
 
@@ -2603,6 +2688,13 @@ static void picolcd_remove(struct hid_device *hdev)
         spin_lock_irqsave(&data->lock, flags);
         data->status |= PICOLCD_FAILED;
         spin_unlock_irqrestore(&data->lock, flags);
+#ifdef CONFIG_HID_PICOLCD_FB
+        /* short-circuit FB as early as possible in order to
+         * avoid long delays if we host console.
+         */
+        if (data->fb_info)
+                data->fb_info->par = NULL;
+#endif
 
         picolcd_exit_devfs(data);
         device_remove_file(&hdev->dev, &dev_attr_operation_mode);
@@ -2660,6 +2752,10 @@ static int __init picolcd_init(void)
 static void __exit picolcd_exit(void)
 {
         hid_unregister_driver(&picolcd_driver);
+#ifdef CONFIG_HID_PICOLCD_FB
+        flush_scheduled_work();
+        WARN_ON(fb_pending);
+#endif
 }
 
 module_init(picolcd_init);