When a fbdev with deferred I/O is once opened and closed, the dirty
pages still remain queued in the pageref list, and eventually later
those may be processed in the delayed work.  This may lead to a
corruption of pages, hitting an Oops.

This patch makes sure to cancel the delayed work and clean up the
pageref list at closing the device for addressing the bug.  A part of
the cleanup code is factored out as a new helper function that is
called from the common fb_release().

Reviewed-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Cc: <redacted>
Signed-off-by: Takashi Iwai <redacted>
---
v1->v2: Fix build error without CONFIG_FB_DEFERRED_IO

  drivers/video/fbdev/core/fb_defio.c | 10 +++++++++-
  drivers/video/fbdev/core/fbmem.c    |  4 ++++
  include/linux/fb.h                  |  1 +
  3 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/video/fbdev/core/fb_defio.c b/drivers/video/fbdev/core/fb_defio.c
index c730253ab85c..583cbcf09446 100644
--- a/drivers/video/fbdev/core/fb_defio.c
+++ b/drivers/video/fbdev/core/fb_defio.c

@@ -313,7 +313,7 @@ void fb_deferred_io_open(struct fb_info *info,
  }
  EXPORT_SYMBOL_GPL(fb_deferred_io_open);
  
-void fb_deferred_io_cleanup(struct fb_info *info)
+void fb_deferred_io_release(struct fb_info *info)
  {
  	struct fb_deferred_io *fbdefio = info->fbdefio;
  	struct page *page;

@@ -327,6 +327,14 @@ void fb_deferred_io_cleanup(struct fb_info *info)
  		page = fb_deferred_io_page(info, i);
  		page->mapping = NULL;
  	}
+}
+EXPORT_SYMBOL_GPL(fb_deferred_io_release);
+
+void fb_deferred_io_cleanup(struct fb_info *info)
+{
+	struct fb_deferred_io *fbdefio = info->fbdefio;
+
+	fb_deferred_io_release(info);
  
  	kvfree(info->pagerefs);
  	mutex_destroy(&fbdefio->lock);

diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
index 3a6c8458eb8d..ab3545a00abc 100644
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c

@@ -1454,6 +1454,10 @@ __releases(&info->lock)
  	struct fb_info * const info = file->private_data;
  
  	lock_fb_info(info);
+#if IS_ENABLED(CONFIG_FB_DEFERRED_IO)
+	if (info->fbdefio)
+		fb_deferred_io_release(info);
+#endif
  	if (info->fbops->fb_release)
  		info->fbops->fb_release(info,1);
  	module_put(info->fbops->owner);

diff --git a/include/linux/fb.h b/include/linux/fb.h
index 96b96323e9cb..73eb1f85ea8e 100644
--- a/include/linux/fb.h
+++ b/include/linux/fb.h

@@ -662,6 +662,7 @@ extern int  fb_deferred_io_init(struct fb_info *info);
  extern void fb_deferred_io_open(struct fb_info *info,
  				struct inode *inode,
  				struct file *file);
+extern void fb_deferred_io_release(struct fb_info *info);
  extern void fb_deferred_io_cleanup(struct fb_info *info);
  extern int fb_deferred_io_fsync(struct file *file, loff_t start,
  				loff_t end, int datasync);