[PATCH 4/4] HID: picolcd: implement refcounting of framebuffer

Bruno Prémont
2010-06-28T20:35:44Z

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>
---
drivers/hid/hid-picolcd.c | 110 ++++++++++++++++++++++++++++++++++++++++++---
1 files changed, 103 insertions(+), 7 deletions(-)

diff --git a/drivers/hid/hid-picolcd.c b/drivers/hid/hid-picolcd.c
index 31a0abd..85a105e 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);
--
1.7.1