On Sun, Jan 20, 2019 at 12:43:18PM +0100, Noralf Trønnes wrote:
> It's now safe to let fbcon unbind automatically on fbdev unregister.
> The crash problem was fixed in commit 2122b40580dd
> ("fbdev: fbcon: Fix unregister crash when more than one framebuffer")
>
> Signed-off-by: Noralf Trønnes <noralf@xxxxxxxxxxx>
> ---
> drivers/gpu/drm/drm_fb_helper.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index 31fcf94bf825..5d0327f603bb 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -2999,7 +2999,8 @@ static int drm_fbdev_fb_open(struct fb_info *info, int user)
> {
> struct drm_fb_helper *fb_helper = info->par;
>
> - if (!try_module_get(fb_helper->dev->driver->fops->owner))
> + /* No need to take a ref for fbcon because it unbinds on unregister */
> + if (user && !try_module_get(fb_helper->dev->driver->fops->owner))
Module refcount != driver refcount. You can always unbind a driver through
the sysfs unbind file, no matter whether the module is pinned or not. So I
think pinng the module is still the right thing to do, just to avoid races
and fun stuff.
btw, I looked into making fbdev hotunplug safe (i.e. drm_dev_enter/exit,
but for fbdev) over the holidays. Fixing that properly for fbdev userspace
clients looks like serious amounts of work, and I think it's impossible
for fbcon. Or at least I didn't come up with a workable idea to sprinkle
the dev_enter/exit stuff around. For the userspace side the basic
infrastructure with get_fb_info() and put_fb_info() is there already.
Cheers, Daniel
> return -ENODEV;
>
> return 0;
> @@ -3009,7 +3010,8 @@ static int drm_fbdev_fb_release(struct fb_info *info, int user)
> {
> struct drm_fb_helper *fb_helper = info->par;
>
> - module_put(fb_helper->dev->driver->fops->owner);
> + if (user)
> + module_put(fb_helper->dev->driver->fops->owner);
>
> return 0;
> }
> --
> 2.20.1
>
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--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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