Deferred I/O was utterly broken. Reading the mmap()ed framebuffer
worked, but writing it made the VM endlessly invoke
vm_ops.page_mkwrite(). That happened because we failed to set
page->mapping and page->index.
The fix is to set them, and clean up properly before the framebuffer
gets released.
Fix extracted from this linux-fbdev-devel message:
Subject: [PATCH 1/1 2.6.24] fbdev: defio and Metronomefb
From: Jaya Kumar <[email protected]>
Date: 2008-02-18 13:41:26
Signed-off-by: Jaya Kumar <[email protected]>
Signed-off-by: Markus Armbruster <[email protected]>
---
drivers/video/fb_defio.c | 22 ++++++++++++++++++++--
1 file changed, 20 insertions(+), 2 deletions(-)
diff --git a/drivers/video/fb_defio.c b/drivers/video/fb_defio.c
index 0f8cfb9..24843fd 100644
--- a/drivers/video/fb_defio.c
+++ b/drivers/video/fb_defio.c
@@ -4,7 +4,7 @@
* Copyright (C) 2006 Jaya Kumar
*
* This file is subject to the terms and conditions of the GNU General Public
- * License. See the file COPYING in the main directory of this archive
+ * License. See the file COPYING in the main directory of this archive
* for more details.
*/
@@ -31,7 +31,7 @@ static int fb_deferred_io_fault(struct vm_area_struct *vma,
unsigned long offset;
struct page *page;
struct fb_info *info = vma->vm_private_data;
- /* info->screen_base is in System RAM */
+ /* info->screen_base is virtual memory */
void *screen_base = (void __force *) info->screen_base;
offset = vmf->pgoff << PAGE_SHIFT;
@@ -43,6 +43,15 @@ static int fb_deferred_io_fault(struct vm_area_struct *vma,
return VM_FAULT_SIGBUS;
get_page(page);
+
+ if (vma->vm_file)
+ page->mapping = vma->vm_file->f_mapping;
+ else
+ printk(KERN_ERR "no mapping available\n");
+
+ BUG_ON(!page->mapping);
+ page->index = vmf->pgoff;
+
vmf->page = page;
return 0;
}
@@ -138,11 +147,20 @@ EXPORT_SYMBOL_GPL(fb_deferred_io_init);
void fb_deferred_io_cleanup(struct fb_info *info)
{
+ void *screen_base = (void __force *) info->screen_base;
struct fb_deferred_io *fbdefio = info->fbdefio;
+ struct page *page;
+ int i;
BUG_ON(!fbdefio);
cancel_delayed_work(&info->deferred_work);
flush_scheduled_work();
+
+ /* clear out the mapping that we setup */
+ for (i = 0 ; i < info->fix.smem_len; i += PAGE_SIZE) {
+ page = vmalloc_to_page(screen_base + i);
+ page->mapping = NULL;
+ }
}
EXPORT_SYMBOL_GPL(fb_deferred_io_cleanup);
On Thu, Feb 21, 2008 at 5:43 PM, Markus Armbruster <[email protected]> wrote:
> Fix extracted from this linux-fbdev-devel message:
Hi Markus,
Yes, this was discussed back in November on linux-mm and hence my
patch. I didn't push for it to be merged by itself because I don't
think it makes sense to merge it separately from the full metronomefb
patch. As far as I can tell, only hecubafb and metronomefb seem to be
the consumers.
Out of curiosity, are you using defio or planning to use it? I would
love to hear back from people who are using it.
Thanks,
jaya
>
> Subject: [PATCH 1/1 2.6.24] fbdev: defio and Metronomefb
> From: Jaya Kumar <[email protected]>
> Date: 2008-02-18 13:41:26
>
> Signed-off-by: Jaya Kumar <[email protected]>
> Signed-off-by: Markus Armbruster <[email protected]>
>
> ---
>
> drivers/video/fb_defio.c | 22 ++++++++++++++++++++--
> 1 file changed, 20 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/video/fb_defio.c b/drivers/video/fb_defio.c
> index 0f8cfb9..24843fd 100644
> --- a/drivers/video/fb_defio.c
> +++ b/drivers/video/fb_defio.c
> @@ -4,7 +4,7 @@
> * Copyright (C) 2006 Jaya Kumar
> *
> * This file is subject to the terms and conditions of the GNU General Public
> - * License. See the file COPYING in the main directory of this archive
> + * License. See the file COPYING in the main directory of this archive
> * for more details.
> */
>
> @@ -31,7 +31,7 @@ static int fb_deferred_io_fault(struct vm_area_struct *vma,
> unsigned long offset;
> struct page *page;
> struct fb_info *info = vma->vm_private_data;
> - /* info->screen_base is in System RAM */
> + /* info->screen_base is virtual memory */
> void *screen_base = (void __force *) info->screen_base;
>
> offset = vmf->pgoff << PAGE_SHIFT;
> @@ -43,6 +43,15 @@ static int fb_deferred_io_fault(struct vm_area_struct *vma,
> return VM_FAULT_SIGBUS;
>
> get_page(page);
> +
> + if (vma->vm_file)
> + page->mapping = vma->vm_file->f_mapping;
> + else
> + printk(KERN_ERR "no mapping available\n");
> +
> + BUG_ON(!page->mapping);
> + page->index = vmf->pgoff;
> +
> vmf->page = page;
> return 0;
> }
> @@ -138,11 +147,20 @@ EXPORT_SYMBOL_GPL(fb_deferred_io_init);
>
> void fb_deferred_io_cleanup(struct fb_info *info)
> {
> + void *screen_base = (void __force *) info->screen_base;
> struct fb_deferred_io *fbdefio = info->fbdefio;
> + struct page *page;
> + int i;
>
> BUG_ON(!fbdefio);
> cancel_delayed_work(&info->deferred_work);
> flush_scheduled_work();
> +
> + /* clear out the mapping that we setup */
> + for (i = 0 ; i < info->fix.smem_len; i += PAGE_SIZE) {
> + page = vmalloc_to_page(screen_base + i);
> + page->mapping = NULL;
> + }
> }
> EXPORT_SYMBOL_GPL(fb_deferred_io_cleanup);
>
>
"Jaya Kumar" <[email protected]> writes:
> On Thu, Feb 21, 2008 at 5:43 PM, Markus Armbruster <[email protected]> wrote:
>> Fix extracted from this linux-fbdev-devel message:
>
> Hi Markus,
>
> Yes, this was discussed back in November on linux-mm and hence my
> patch. I didn't push for it to be merged by itself because I don't
> think it makes sense to merge it separately from the full metronomefb
> patch. As far as I can tell, only hecubafb and metronomefb seem to be
> the consumers.
>
> Out of curiosity, are you using defio or planning to use it? I would
> love to hear back from people who are using it.
>
> Thanks,
> jaya
Converting to fb_defio made xen-fbfront quite a bit simpler and much
more maintainable. Excellent match.
It took me a bit of time to find your fix, mostly because I assumed my
own code was broken, not fb_defio. It's best not to make assumptions
about who uses your code; if it's any good, chances are somebody will
find a use you never imagined.