Re: [PATCH v2 09/19] fbcon: Extract fbcon_open/release helpers

Daniel Vetter
2022-04-05T12:16:52Z

On Thu, Feb 10, 2022 at 12:46:32PM +0100, Thomas Zimmermann wrote:
> Hi
>
> Am 08.02.22 um 22:08 schrieb Daniel Vetter:
> > 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.
> >
> > Note that everything in fbcon.c is protected by the big console_lock()
> > lock (especially all the global variables), so the minor changes in
> > ordering of setup/cleanup do not matter.
> >
> > v2: Explain a bit better why this is all correct (Sam)
> >
> > Acked-by: Sam Ravnborg <sam@ravnborg.org>
> > 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 058e885d24f6..3e1a3e7bf527 100644
> > --- a/drivers/video/fbdev/core/fbcon.c
> > +++ b/drivers/video/fbdev/core/fbcon.c
> > @@ -682,19 +682,37 @@ 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);
> > @@ -715,7 +733,7 @@ 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;
> > @@ -726,45 +744,34 @@ 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;
>
> We don't need oldidx any longer?
>
> There's some logic wrt to the parameter 'found' here and in set_con2fb_map()
> that appears to be relevant.

Yeah further patches clean this up more. Or did you see a potential bug
here? I did ditch the fb_release error handling, simply because there's
not really much we can do anyway, it shouldn't ever fail (that's a driver
bug) and it was convoluting the code for no gain. But I might have missed
something in this cargo-cult.
-Daniel

>
> Best regards
> Thomas
>
>
> > - 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;
> > + /*
> > + 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,
> > @@ -919,7 +926,6 @@ 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;
> > @@ -938,17 +944,12 @@ 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;
> > }
> > @@ -3314,10 +3315,6 @@ 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;
> > @@ -3327,6 +3324,8 @@ static void fbcon_exit(void)
> > kfree(info->fbcon_par);
> > info->fbcon_par = NULL;
> > }
> > +
> > + fbcon_release(info);
> > }
> > }
> > }
>
> --
> Thomas Zimmermann
> Graphics Driver Developer
> SUSE Software Solutions Germany GmbH
> Maxfeldstr. 5, 90409 Nürnberg, Germany
> (HRB 36809, AG Nürnberg)
> Geschäftsführer: Ivo Totev

--
Daniel Vetter
Software Engineer, Intel Corporation