Re: [PATCH v2] fb_defio: Remove custom address_space_operations

Daniel Vetter
2021-06-01T15:39:31Z

On Tue, Jun 01, 2021 at 03:30:30PM +0100, Matthew Wilcox wrote:
> 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?

Thanks, that worked with Link: and everything and no choking of my script
:-)

Cheers, Daniel

> 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
>

--
Daniel Vetter
Software Engineer, Intel Corporation