Re: [PATCH] fbdefio: add set_page_dirty handler to deferred IO FB

[Ian Campbell]

[correcting stable@]

On Wed, 2008-08-20 at 01:37 -0700, Andrew Morton wrote:
> On Wed, 20 Aug 2008 09:13:23 +0100 Ian Campbell <ijc@xxxxxxxxxxxxxx> wrote:
> 
> > Perhaps applying the band-aid at open time instead would be preferred?
> 
> That would be less racy, I expect.
[...]
> <tries to write a patch>
> 
> OK, seems that fb_ops.fb_open() has no way of getting at the `struct
> file *' which is being opened (wtf?).  Screwed.  Need to change
> fb_ops.fb_open(), or add a new fb_ops.fb_open_sane().

Ah yes, I remember why I did it in mmap() now...

How about this version? Not as clean as overriding fb_open() but
involves less frobbing with unrelated drivers.

From ae2f7f118518fbfd4006c985b136a5d3d1a314af Mon Sep 17 00:00:00 2001
From: Ian Campbell <ijc@xxxxxxxxxxxxxx>
Date: Wed, 20 Aug 2008 19:54:50 +0100
Subject: [PATCH] fbdefio: add set_page_dirty handler to deferred IO FB

Fixes kernel BUG at lib/radix-tree.c:473.

Previously the handler was incidentally provided by tmpfs but this was
removed with:

  commit 14fcc23fdc78e9d32372553ccf21758a9bd56fa1
  Author: Hugh Dickins <hugh@xxxxxxxxxxx>
  Date:   Mon Jul 28 15:46:19 2008 -0700

    tmpfs: fix kernel BUG in shmem_delete_inode

relying on this behaviour was incorrect in any case and the BUG
also appeared when the device node was on an ext3 filesystem.

v2: override a_ops at open() time rather than mmap() time to minimise
races per AKPM's concerns.

Signed-off-by: Ian Campbell <ijc@xxxxxxxxxxxxxx>
Acked-by: Jaya Kumar <jayakumar.lkml@xxxxxxxxx>
Acked-by: Nick Piggin <npiggin@xxxxxxx>
Acked-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Jaya Kumar <jayakumar.lkml@xxxxxxxxx>
Cc: Nick Piggin <npiggin@xxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Hugh Dickins <hugh@xxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxxx>
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Cc: Kel Modderman <kel@xxxxxxxxxx>
Cc: Markus Armbruster <armbru@xxxxxxxxxx>
Cc: stable@xxxxxxxxxx [14fcc23fd is in 2.6.25.14 and 2.6.26.1]
---
 drivers/video/fb_defio.c |   19 +++++++++++++++++++
 drivers/video/fbmem.c    |    4 ++++
 include/linux/fb.h       |    3 +++
 3 files changed, 26 insertions(+), 0 deletions(-)

diff --git a/drivers/video/fb_defio.c b/drivers/video/fb_defio.c
index 59df132..4835bdc 100644
--- a/drivers/video/fb_defio.c
+++ b/drivers/video/fb_defio.c
@@ -114,6 +114,17 @@ static struct vm_operations_struct fb_deferred_io_vm_ops = {
 	.page_mkwrite	= fb_deferred_io_mkwrite,
 };
 
+static int fb_deferred_io_set_page_dirty(struct page *page)
+{
+	if (!PageDirty(page))
+		SetPageDirty(page);
+	return 0;
+}
+
+static const struct address_space_operations fb_deferred_io_aops = {
+	.set_page_dirty = fb_deferred_io_set_page_dirty,
+};
+
 static int fb_deferred_io_mmap(struct fb_info *info, struct vm_area_struct *vma)
 {
 	vma->vm_ops = &fb_deferred_io_vm_ops;
@@ -163,6 +174,14 @@ void fb_deferred_io_init(struct fb_info *info)
 }
 EXPORT_SYMBOL_GPL(fb_deferred_io_init);
 
+void fb_deferred_io_open(struct fb_info *info,
+			 struct inode *inode,
+			 struct file *file)
+{
+	file->f_mapping->a_ops = &fb_deferred_io_aops;
+}
+EXPORT_SYMBOL_GPL(fb_deferred_io_open);
+
 void fb_deferred_io_cleanup(struct fb_info *info)
 {
 	void *screen_base = (void __force *) info->screen_base;
diff --git a/drivers/video/fbmem.c b/drivers/video/fbmem.c
index 6b48780..98843c2 100644
--- a/drivers/video/fbmem.c
+++ b/drivers/video/fbmem.c
@@ -1344,6 +1344,10 @@ fb_open(struct inode *inode, struct file *file)
 		if (res)
 			module_put(info->fbops->owner);
 	}
+#ifdef CONFIG_FB_DEFERRED_IO
+	if (info->fbdefio)
+		fb_deferred_io_open(info, inode, file);
+#endif
 out:
 	unlock_kernel();
 	return res;
diff --git a/include/linux/fb.h b/include/linux/fb.h
index 3b8870e..531ccd5 100644
--- a/include/linux/fb.h
+++ b/include/linux/fb.h
@@ -976,6 +976,9 @@ static inline void __fb_pad_aligned_buffer(u8 *dst, u32 d_pitch,
 
 /* drivers/video/fb_defio.c */
 extern void 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_cleanup(struct fb_info *info);
 extern int fb_deferred_io_fsync(struct file *file, struct dentry *dentry,
 				int datasync);
-- 
1.5.6.3




-- 
Ian Campbell

Hope that the day after you die is a nice day.

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