Re: [PATCH 01/13] video: fb_defio: preserve user fb_ops
From: Ville Syrjälä <hidden>
Date: 2019-11-27 17:01:16
Also in:
dri-devel, intel-gfx
On Wed, Nov 27, 2019 at 06:31:57PM +0200, Jani Nikula wrote:
Modifying fb_ops directly to override fb_mmap with fb_deferred_io_mmap and then resetting it to NULL afterwards causes problems all over the place. First, it prevents making the fbops member of struct fb_info a const pointer, which means we can't make struct fb_ops const anywhere. Second, a few places have to go out of their way to restore the original fb_mmap pointer that gets reset to NULL. Preserve the passed in fb_ops by making a copy of it and modifying that instead. Add a deferred_io_private member to struct fb_info to store the pointer to the old fb_ops, and restore that at cleanup.
Quite the horror show. I wonder how hard it would be to just have each
driver that can use defio provide a mmap hook that either dispatches
to the defio one or the native one depending if defio is used or not...
A few drivers at least seem to always use defio so those should be
trivial. Some others seem to make the decision dynamically, which
would require custom .mmap(). Though I suppose all of them could just
be of the form
foo_mmap_wrap{)
{
if (info->defio)
defio_mmap()
else
foo_mmap();
}
Hmm. Actually is .fb_mmap() called from anywhere but fb_mmap()? If not
we could just shove the defio check there? Or if it's called from
several places we could try to wrap all calls in _fb_mmap() or somesuch.
quoted hunk ↗ jump to hunk
Cc: Jaya Kumar <jayalk@intworks.biz> Cc: linux-fbdev@vger.kernel.org Signed-off-by: Jani Nikula <redacted> --- Note: If the approach is acceptable, we'll also need to handle the error returns on memory allocation failures at fb_deferred_io_init() call sites. There are 13. --- drivers/video/fbdev/core/fb_defio.c | 25 ++++++++++++++++++++++--- include/linux/fb.h | 3 ++- 2 files changed, 24 insertions(+), 4 deletions(-)diff --git a/drivers/video/fbdev/core/fb_defio.c b/drivers/video/fbdev/core/fb_defio.c index 82c20c6047b0..36697844c1e0 100644 --- a/drivers/video/fbdev/core/fb_defio.c +++ b/drivers/video/fbdev/core/fb_defio.c@@ -200,13 +200,23 @@ static void fb_deferred_io_work(struct work_struct *work) mutex_unlock(&fbdefio->lock); } -void fb_deferred_io_init(struct fb_info *info) +int fb_deferred_io_init(struct fb_info *info) { struct fb_deferred_io *fbdefio = info->fbdefio; + struct fb_ops *fbops; BUG_ON(!fbdefio); + + fbops = kmemdup(info->fbops, sizeof(*fbops), GFP_KERNEL); + if (!fbops) + return -ENOMEM; + + fbops->fb_mmap = fb_deferred_io_mmap; + info->deferred_io_private = info->fbops; + info->fbops = fbops; + mutex_init(&fbdefio->lock); - info->fbops->fb_mmap = fb_deferred_io_mmap; + INIT_DELAYED_WORK(&info->deferred_work, fb_deferred_io_work); INIT_LIST_HEAD(&fbdefio->pagelist); if (fbdefio->delay = 0) /* set a default of 1 s */@@ -229,6 +239,12 @@ void fb_deferred_io_cleanup(struct fb_info *info) int i; BUG_ON(!fbdefio); + + /* sanity check against misuse */ + if (WARN_ON(!info->deferred_io_private || + info->fbops->fb_mmap != fb_deferred_io_mmap)) + return; + cancel_delayed_work_sync(&info->deferred_work); /* clear out the mapping that we setup */@@ -237,7 +253,10 @@ void fb_deferred_io_cleanup(struct fb_info *info) page->mapping = NULL; } - info->fbops->fb_mmap = NULL; + kfree(info->fbops); + info->fbops = info->deferred_io_private; + info->deferred_io_private = NULL; + mutex_destroy(&fbdefio->lock); } EXPORT_SYMBOL_GPL(fb_deferred_io_cleanup);diff --git a/include/linux/fb.h b/include/linux/fb.h index a6ad528990de..65f2abd47745 100644 --- a/include/linux/fb.h +++ b/include/linux/fb.h@@ -470,6 +470,7 @@ struct fb_info { #ifdef CONFIG_FB_DEFERRED_IO struct delayed_work deferred_work; struct fb_deferred_io *fbdefio; + void *deferred_io_private; #endif struct fb_ops *fbops;@@ -658,7 +659,7 @@ 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 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);-- 2.20.1
-- Ville Syrjälä Intel