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Subject[PATCH v3 06/11] fblog: open fb on registration
Date
This opens the framebuffer upon registration so we can use it for
drawing-operations. On unregistration we close it again.

While opening/closing or accessing the fb in any other way, we must hold
the fb-mutex. However, since the notifiers are often called with the mutex
already held, we cannot lock it _after_ taking the
fblog_registration_lock. Therefore, we require the caller to make sure the
fb-mutex is held.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
---
drivers/video/console/fblog.c | 94 ++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 93 insertions(+), 1 deletion(-)
diff --git a/drivers/video/console/fblog.c b/drivers/video/console/fblog.c
index 279f4d8..1c526c5 100644
--- a/drivers/video/console/fblog.c
+++ b/drivers/video/console/fblog.c
@@ -32,12 +32,14 @@

enum fblog_flags {
FBLOG_KILLED,
+ FBLOG_OPEN,
};

struct fblog_fb {
unsigned long flags;
struct fb_info *info;
struct device dev;
+ struct mutex lock;
};

static DEFINE_MUTEX(fblog_registration_lock);
@@ -46,6 +48,74 @@ static struct fblog_fb *fblog_fbs[FB_MAX];
#define to_fblog_dev(_d) container_of(_d, struct fblog_fb, dev)

/*
+ * fblog_open/close()
+ * These functions manage access to the underlying framebuffer. While opened, we
+ * have a valid reference to the fb and can use it for drawing operations. When
+ * the fb is unregistered, we drop our reference and close the fb so it can get
+ * deleted properly. We also mark it as dead so no further fblog_open() call
+ * will succeed.
+ * Both functions must be called with the fb->info->lock mutex held! But make
+ * sure to lock it _before_ locking the fblog-registration-lock. Otherwise, we
+ * will dead-lock with fb-registration.
+ */
+
+static int fblog_open(struct fblog_fb *fb)
+{
+ int ret;
+
+ mutex_lock(&fb->lock);
+
+ if (test_bit(FBLOG_KILLED, &fb->flags)) {
+ ret = -ENODEV;
+ goto unlock;
+ }
+
+ if (test_bit(FBLOG_OPEN, &fb->flags)) {
+ ret = 0;
+ goto unlock;
+ }
+
+ if (!try_module_get(fb->info->fbops->owner)) {
+ ret = -ENODEV;
+ goto out_killed;
+ }
+
+ if (fb->info->fbops->fb_open && fb->info->fbops->fb_open(fb->info, 0)) {
+ ret = -EIO;
+ goto out_unref;
+ }
+
+ set_bit(FBLOG_OPEN, &fb->flags);
+ mutex_unlock(&fb->lock);
+ return 0;
+
+out_unref:
+ module_put(fb->info->fbops->owner);
+out_killed:
+ set_bit(FBLOG_KILLED, &fb->flags);
+unlock:
+ mutex_unlock(&fb->lock);
+ return ret;
+}
+
+static void fblog_close(struct fblog_fb *fb, bool kill_dev)
+{
+ mutex_lock(&fb->lock);
+
+ if (test_bit(FBLOG_OPEN, &fb->flags)) {
+ if (fb->info->fbops->fb_release)
+ fb->info->fbops->fb_release(fb->info, 0);
+ module_put(fb->info->fbops->owner);
+ clear_bit(FBLOG_OPEN, &fb->flags);
+ }
+
+ if (kill_dev)
+ set_bit(FBLOG_KILLED, &fb->flags);
+
+ mutex_unlock(&fb->lock);
+}
+
+/*
* fblog framebuffer list
* The fblog_fbs[] array contains all currently registered framebuffers. If a
* framebuffer is in that list, we always must make sure that we own a reference
@@ -77,6 +147,7 @@ static void fblog_do_unregister(struct fb_info *info)

fblog_fbs[info->node] = NULL;

+ fblog_close(fb, true);
device_del(&fb->dev);
put_device(&fb->dev);
}
@@ -99,6 +170,7 @@ static void fblog_do_register(struct fb_info *info, bool force)
return;

fb->info = info;
+ mutex_init(&fb->lock);
__module_get(THIS_MODULE);
device_initialize(&fb->dev);
fb->dev.class = fb_class;
@@ -113,6 +185,8 @@ static void fblog_do_register(struct fb_info *info, bool force)
put_device(&fb->dev);
return;
}
+
+ fblog_open(fb);
}

static void fblog_register(struct fb_info *info, bool force)
@@ -134,6 +208,7 @@ static int fblog_event(struct notifier_block *self, unsigned long action,
{
struct fb_event *event = data;
struct fb_info *info = event->info;
+ struct fblog_fb *fb;

switch(action) {
case FB_EVENT_FB_REGISTERED:
@@ -145,8 +220,21 @@ static int fblog_event(struct notifier_block *self, unsigned long action,
case FB_EVENT_FB_UNREGISTERED:
/* This is called when a low-level system driver unregisters a
* framebuffer. The registration lock is held but the console
- * lock might not be held. */
+ * lock might not be held. The fb-lock is not held, either! */
+ mutex_lock(&info->lock);
fblog_unregister(info);
+ mutex_unlock(&info->lock);
+ break;
+ case FB_EVENT_FB_UNBIND:
+ /* Called directly before unregistering an FB. The FB is still
+ * valid here and the registration lock is held but the console
+ * lock might not be held (really?). */
+ mutex_lock(&fblog_registration_lock);
+ fb = fblog_fbs[info->node];
+ mutex_unlock(&fblog_registration_lock);
+
+ if (fb)
+ fblog_close(fb, true);
break;
}

@@ -163,7 +251,9 @@ static void fblog_scan(void)
if (!info || IS_ERR(info))
continue;

+ mutex_lock(&info->lock);
fblog_register(info, false);
+ mutex_unlock(&info->lock);

/* There is a very subtle race-condition. Even though we might
* own a reference to the fb, it may still get unregistered
@@ -224,7 +314,9 @@ static void __exit fblog_exit(void)
if (!info || IS_ERR(info))
continue;

+ mutex_lock(&info->lock);
fblog_unregister(info);
+ mutex_unlock(&info->lock);
put_fb_info(info);
}
}
--
1.7.11.2


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