Re: [Intel-gfx] [PATCH 11/21] fbcon: Extract fbcon_open/release helpers

Daniel Vetter
2022-02-08T13:48:35Z

On Thu, Feb 03, 2022 at 10:15:14PM +0100, Sam Ravnborg wrote:
> Hi Daniel,
>
> On Mon, Jan 31, 2022 at 10:05:42PM +0100, Daniel Vetter wrote:
> > There's two minor behaviour changes in here:
> > - in error paths we now consistently call fb_ops->fb_release
> > - fb_release really can't fail (fbmem.c ignores it too) and there's no
> > reasonable cleanup we can do anyway.
> >
> > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> > Cc: Daniel Vetter <daniel@ffwll.ch>
> > Cc: Claudio Suarez <cssk@net-c.es>
> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> > Cc: Du Cheng <ducheng2@gmail.com>
> > ---
> > drivers/video/fbdev/core/fbcon.c | 107 +++++++++++++++----------------
> > 1 file changed, 53 insertions(+), 54 deletions(-)
> >
> > diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
> > index fa30e1909164..eea2ee14b64c 100644
> > --- a/drivers/video/fbdev/core/fbcon.c
> > +++ b/drivers/video/fbdev/core/fbcon.c
> > @@ -680,19 +680,37 @@ static int fbcon_invalid_charcount(struct fb_info *info, unsigned charcount)
> >
> > #endif /* CONFIG_MISC_TILEBLITTING */
> >
> > +static int fbcon_open(struct fb_info *info)
> > +{
> > + if (!try_module_get(info->fbops->owner))
> > + return -ENODEV;
> > +
> > + if (info->fbops->fb_open &&
> > + info->fbops->fb_open(info, 0)) {
> > + module_put(info->fbops->owner);
> > + return -ENODEV;
> > + }
> > +
> > + return 0;
> > +}
> > +
> > +static void fbcon_release(struct fb_info *info)
> > +{
> > + if (info->fbops->fb_release)
> > + info->fbops->fb_release(info, 0);
> > +
> > + module_put(info->fbops->owner);
> > +}
> >
> > static int con2fb_acquire_newinfo(struct vc_data *vc, struct fb_info *info,
> > int unit, int oldidx)
> > {
> > struct fbcon_ops *ops = NULL;
> > - int err = 0;
> > -
> > - if (!try_module_get(info->fbops->owner))
> > - err = -ENODEV;
> > + int err;
> >
> > - if (!err && info->fbops->fb_open &&
> > - info->fbops->fb_open(info, 0))
> > - err = -ENODEV;
> > + err = fbcon_open(info);
> > + if (err)
> > + return err;
> >
> > if (!err) {
> > ops = kzalloc(sizeof(struct fbcon_ops), GFP_KERNEL);
> > @@ -713,7 +731,7 @@ static int con2fb_acquire_newinfo(struct vc_data *vc, struct fb_info *info,
> >
> > if (err) {
> > con2fb_map[unit] = oldidx;
> > - module_put(info->fbops->owner);
> > + fbcon_release(info);
> > }
> >
> > return err;
> > @@ -724,45 +742,34 @@ static int con2fb_release_oldinfo(struct vc_data *vc, struct fb_info *oldinfo,
> > int oldidx, int found)
> > {
> > struct fbcon_ops *ops = oldinfo->fbcon_par;
> > - int err = 0, ret;
> > + int ret;
> >
> > - if (oldinfo->fbops->fb_release &&
> > - oldinfo->fbops->fb_release(oldinfo, 0)) {
> > - con2fb_map[unit] = oldidx;
> The old code assigns con2fb_map[unit] before is calls
> newinfo->fbops->fb_release).
> I wonder if there can be any callback to fbcon where the value
> of con2fb_map[unit] matters?

It's all protected by console_lock, so other threads cannot see the
inconsistent state.

Essentially everything in fbcon.c is protected by console_lock().

Do you want me to hammer this in somewhere (maybe in the commit message),
or good enough for your ack?
-Daniel

>
>
> > - if (!found && newinfo->fbops->fb_release)
> > - newinfo->fbops->fb_release(newinfo, 0);
> > - if (!found)
> > - module_put(newinfo->fbops->owner);
> > - err = -ENODEV;
> > - }
> > + fbcon_release(oldinfo);
> >
> > - if (!err) {
> > - fbcon_del_cursor_work(oldinfo);
> > - kfree(ops->cursor_state.mask);
> > - kfree(ops->cursor_data);
> > - kfree(ops->cursor_src);
> > - kfree(ops->fontbuffer);
> > - kfree(oldinfo->fbcon_par);
> > - oldinfo->fbcon_par = NULL;
> > - module_put(oldinfo->fbops->owner);
> > - /*
> > - If oldinfo and newinfo are driving the same hardware,
> > - the fb_release() method of oldinfo may attempt to
> > - restore the hardware state. This will leave the
> > - newinfo in an undefined state. Thus, a call to
> > - fb_set_par() may be needed for the newinfo.
> > - */
> > - if (newinfo && newinfo->fbops->fb_set_par) {
> > - ret = newinfo->fbops->fb_set_par(newinfo);
> > + fbcon_del_cursor_work(oldinfo);
>
>
> > + kfree(ops->cursor_state.mask);
> > + kfree(ops->cursor_data);
> > + kfree(ops->cursor_src);
> > + kfree(ops->fontbuffer);
> > + kfree(oldinfo->fbcon_par);
> > + oldinfo->fbcon_par = NULL;
> These all look like candidates to stuff into fbcon_release()
> That would drop the nice symmetry but make it more consistent.
>
> I think we miss freeing ops->cursor_data in fbcon_exit(),
> but I did not follow all the code.
>
> With my ramblings considered the patch is
> Acked-by: Sam Ravnborg <sam@ravnborg.org>
>
> Sam
>
> > + /*
> > + If oldinfo and newinfo are driving the same hardware,
> > + the fb_release() method of oldinfo may attempt to
> > + restore the hardware state. This will leave the
> > + newinfo in an undefined state. Thus, a call to
> > + fb_set_par() may be needed for the newinfo.
> > + */
> > + if (newinfo && newinfo->fbops->fb_set_par) {
> > + ret = newinfo->fbops->fb_set_par(newinfo);
> >
> > - if (ret)
> > - printk(KERN_ERR "con2fb_release_oldinfo: "
> > - "detected unhandled fb_set_par error, "
> > - "error code %d\n", ret);
> > - }
> > + if (ret)
> > + printk(KERN_ERR "con2fb_release_oldinfo: "
> > + "detected unhandled fb_set_par error, "
> > + "error code %d\n", ret);
> > }
> >
> > - return err;
> > + return 0;
> > }
> >
> > static void con2fb_init_display(struct vc_data *vc, struct fb_info *info,
> > @@ -917,7 +924,6 @@ static const char *fbcon_startup(void)
> > struct fbcon_display *p = &fb_display[fg_console];
> > struct vc_data *vc = vc_cons[fg_console].d;
> > const struct font_desc *font = NULL;
> > - struct module *owner;
> > struct fb_info *info = NULL;
> > struct fbcon_ops *ops;
> > int rows, cols;
> > @@ -936,17 +942,12 @@ static const char *fbcon_startup(void)
> > if (!info)
> > return NULL;
> >
> > - owner = info->fbops->owner;
> > - if (!try_module_get(owner))
> > + if (fbcon_open(info))
> > return NULL;
> > - if (info->fbops->fb_open && info->fbops->fb_open(info, 0)) {
> > - module_put(owner);
> > - return NULL;
> > - }
> >
> > ops = kzalloc(sizeof(struct fbcon_ops), GFP_KERNEL);
> > if (!ops) {
> > - module_put(owner);
> > + fbcon_release(info);
> > return NULL;
> > }
> >
> > @@ -3331,10 +3332,6 @@ static void fbcon_exit(void)
> > }
> >
> > if (mapped) {
> > - if (info->fbops->fb_release)
> > - info->fbops->fb_release(info, 0);
> > - module_put(info->fbops->owner);
> > -
> > if (info->fbcon_par) {
> > struct fbcon_ops *ops = info->fbcon_par;
> >
> > @@ -3344,6 +3341,8 @@ static void fbcon_exit(void)
> > kfree(info->fbcon_par);
> > info->fbcon_par = NULL;
> > }
> > +
> > + fbcon_release(info);
> > }
> > }
> > }
> > --
> > 2.33.0

--
Daniel Vetter
Software Engineer, Intel Corporation