Re: [PATCH v2] fb_defio: Remove custom address_space_operations

Matthew Wilcox
2021-06-01T14:30:39Z

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On Tue, Jun 01, 2021 at 04:10:32PM +0200, Daniel Vetter wrote:
> On Sun, May 30, 2021 at 10:14:22PM +0100, Matthew Wilcox wrote:
> > On Sun, May 30, 2021 at 12:13:05PM -0700, Nathan Chancellor wrote:
> > > Hi Matthew,
> > >
> > > On Wed, Mar 10, 2021 at 06:55:30PM +0000, Matthew Wilcox (Oracle) wrote:
> > > > There's no need to give the page an address_space. Leaving the
> > > > page->mapping as NULL will cause the VM to handle set_page_dirty()
> > > > the same way that it's handled now, and that was the only reason to
> > > > set the address_space in the first place.
> > > >
> > > > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> > > > Reviewed-by: Christoph Hellwig <hch@lst.de>
> > > > Reviewed-by: William Kucharski <william.kucharski@oracle.com>
> > >
> > > This patch in mainline as commit ccf953d8f3d6 ("fb_defio: Remove custom
> > > address_space_operations") causes my Hyper-V based VM to no longer make
> > > it to a graphical environment.
> >
> > Hi Nathan,
> >
> > Thanks for the report. I sent Daniel a revert patch with a full
> > explanation last week, which I assume he'll queue up for a pull soon.
> > You can just git revert ccf953d8f3d6 for yourself until that shows up.
> > Sorry for the inconvenience.
>
> Uh that patch didn't get cc'ed to any list so I've ignored it. I've found
> it now, but lack of lore link is awkward. Can you pls resubmit with
> dri-devel on cc? fbdev list is dead, I don't look there.

How about I just attach it here?

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From e88921d0775d87323a8688af37dfd7cdebdde5a9 Mon Sep 17 00:00:00 2001
From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Date: Tue, 25 May 2021 08:37:33 -0400
Subject: [PATCH] Revert "fb_defio: Remove custom address_space_operations"

Commit ccf953d8f3d6 makes framebuffers which use deferred I/O stop
displaying updates after the first one. This is because the pages
handled by fb_defio no longer have a page_mapping(). That prevents
page_mkclean() from marking the PTEs as clean, and so writes are only
noticed the first time.

Reported-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
drivers/video/fbdev/core/fb_defio.c | 35 +++++++++++++++++++++++++++++
drivers/video/fbdev/core/fbmem.c | 4 ++++
include/linux/fb.h | 3 +++
3 files changed, 42 insertions(+)

diff --git a/drivers/video/fbdev/core/fb_defio.c b/drivers/video/fbdev/core/fb_defio.c
index b292887a2481..a591d291b231 100644
--- a/drivers/video/fbdev/core/fb_defio.c
+++ b/drivers/video/fbdev/core/fb_defio.c
@@ -52,6 +52,13 @@ static vm_fault_t fb_deferred_io_fault(struct vm_fault *vmf)
return VM_FAULT_SIGBUS;

get_page(page);
+
+ if (vmf->vma->vm_file)
+ page->mapping = vmf->vma->vm_file->f_mapping;
+ else
+ printk(KERN_ERR "no mapping available\n");
+
+ BUG_ON(!page->mapping);
page->index = vmf->pgoff;

vmf->page = page;
@@ -144,6 +151,17 @@ static const 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,
+};
+
int fb_deferred_io_mmap(struct fb_info *info, struct vm_area_struct *vma)
{
vma->vm_ops = &fb_deferred_io_vm_ops;
@@ -194,12 +212,29 @@ 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)
{
struct fb_deferred_io *fbdefio = info->fbdefio;
+ struct page *page;
+ int i;

BUG_ON(!fbdefio);
cancel_delayed_work_sync(&info->deferred_work);
+
+ /* clear out the mapping that we setup */
+ for (i = 0 ; i < info->fix.smem_len; i += PAGE_SIZE) {
+ page = fb_deferred_io_page(info, i);
+ page->mapping = NULL;
+ }
+
mutex_destroy(&fbdefio->lock);
}
EXPORT_SYMBOL_GPL(fb_deferred_io_cleanup);
diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
index 072780b0e570..98f193078c05 100644
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -1415,6 +1415,10 @@ __releases(&info->lock)
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_fb_info(info);
if (res)
diff --git a/include/linux/fb.h b/include/linux/fb.h
index a8dccd23c249..ecfbcc0553a5 100644
--- a/include/linux/fb.h
+++ b/include/linux/fb.h
@@ -659,6 +659,9 @@ static inline void __fb_pad_aligned_buffer(u8 *dst, u32 d_pitch,
/* drivers/video/fb_defio.c */
int fb_deferred_io_mmap(struct fb_info *info, struct vm_area_struct *vma);
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, loff_t start,
loff_t end, int datasync);
--
2.30.2