Re: [PATCH 16/21] fbcon: Move console_lock for register/unlink/unregister

Daniel Vetter
2022-02-08T13:56:41Z

On Fri, Feb 04, 2022 at 08:54:24PM +0100, Sam Ravnborg wrote:
> Hi Daniel.
>
> On Mon, Jan 31, 2022 at 10:05:47PM +0100, Daniel Vetter wrote:
> > Ideally console_lock becomes an implementation detail of fbcon.c and
> > doesn't show up anywhere in fbmem.c. We're still pretty far from that,
> > but at least the register/unregister code is there now.
> >
> > With this the do_fb_ioctl() handler is the only code in fbmem.c still
> > calling console_lock().
> >
> > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> > Cc: Daniel Vetter <daniel@ffwll.ch>
> > Cc: Thomas Zimmermann <tzimmermann@suse.de>
> > Cc: Du Cheng <ducheng2@gmail.com>
> > 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: Matthew Wilcox <willy@infradead.org>
> > Cc: Sam Ravnborg <sam@ravnborg.org>
> > Cc: Zheyu Ma <zheyuma97@gmail.com>
> > Cc: Guenter Roeck <linux@roeck-us.net>
> > Cc: Alex Deucher <alexander.deucher@amd.com>
> > Cc: Zhen Lei <thunder.leizhen@huawei.com>
> > Cc: Xiyu Yang <xiyuyang19@fudan.edu.cn>
>
> Like how lock_console is now almost local to fbcon.
> Except the usage outside fbmem + fbcon taht is.

Yeah that's the goal. The problem is that moving console_lock for the
remaining fb_pan and fb_set_var calls will mean we need to put
lock_fbinfo() calls into fbcon.c, and right now that's just not
impossible. The FIXME update at the end of the series tries to explain
this a bit more.
-Daniel

>
> Acked-by: Sam Ravnborg <sam@ravnborg.org>
>
> > ---
> > drivers/video/fbdev/core/fbcon.c | 33 ++++++++++++++++++++++++++------
> > drivers/video/fbdev/core/fbmem.c | 23 ++--------------------
> > 2 files changed, 29 insertions(+), 27 deletions(-)
> >
> > diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
> > index 11b9f962af6f..e5e8aaf6f60d 100644
> > --- a/drivers/video/fbdev/core/fbcon.c
> > +++ b/drivers/video/fbdev/core/fbcon.c
> > @@ -2776,10 +2776,12 @@ void fbcon_fb_unbind(struct fb_info *info)
> > int i, new_idx = -1;
> > int idx = info->node;
> >
> > - WARN_CONSOLE_UNLOCKED();
> > + console_lock();
> >
> > - if (!fbcon_has_console_bind)
> > + if (!fbcon_has_console_bind) {
> > + console_unlock();
> > return;
> > + }
> >
> > for (i = first_fb_vc; i <= last_fb_vc; i++) {
> > if (con2fb_map[i] != idx &&
> > @@ -2814,6 +2816,8 @@ void fbcon_fb_unbind(struct fb_info *info)
> > }
> > fbcon_unbind();
> > }
> > +
> > + console_unlock();
> > }
> >
> > /* called with console_lock held */
> > @@ -2821,10 +2825,12 @@ void fbcon_fb_unregistered(struct fb_info *info)
> > {
> > int i, idx;
> >
> > - WARN_CONSOLE_UNLOCKED();
> > + console_lock();
> >
> > - if (deferred_takeover)
> > + if (deferred_takeover) {
> > + console_unlock();
> > return;
> > + }
> >
> > idx = info->node;
> > for (i = first_fb_vc; i <= last_fb_vc; i++) {
> > @@ -2853,6 +2859,7 @@ void fbcon_fb_unregistered(struct fb_info *info)
> >
> > if (!num_registered_fb)
> > do_unregister_con_driver(&fb_con);
> > + console_unlock();
> > }
> >
> > void fbcon_remap_all(struct fb_info *info)
> > @@ -2910,19 +2917,27 @@ static inline void fbcon_select_primary(struct fb_info *info)
> > }
> > #endif /* CONFIG_FRAMEBUFFER_DETECT_PRIMARY */
> >
> > +static bool lockless_register_fb;
> > +module_param_named_unsafe(lockless_register_fb, lockless_register_fb, bool, 0400);
> > +MODULE_PARM_DESC(lockless_register_fb,
> > + "Lockless framebuffer registration for debugging [default=off]");
> > +
> > /* called with console_lock held */
> > int fbcon_fb_registered(struct fb_info *info)
> > {
> > int ret = 0, i, idx;
> >
> > - WARN_CONSOLE_UNLOCKED();
> > + if (!lockless_register_fb)
> > + console_lock();
> > + else
> > + atomic_inc(&ignore_console_lock_warning);
> >
> > idx = info->node;
> > fbcon_select_primary(info);
> >
> > if (deferred_takeover) {
> > pr_info("fbcon: Deferring console take-over\n");
> > - return 0;
> > + goto out;
> > }
> >
> > if (info_idx == -1) {
> > @@ -2942,6 +2957,12 @@ int fbcon_fb_registered(struct fb_info *info)
> > }
> > }
> >
> > +out:
> > + if (!lockless_register_fb)
> > + console_unlock();
> > + else
> > + atomic_dec(&ignore_console_lock_warning);
> > +
> > return ret;
> > }
> >
> > diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
> > index fd51d12f2702..904ef1250677 100644
> > --- a/drivers/video/fbdev/core/fbmem.c
> > +++ b/drivers/video/fbdev/core/fbmem.c
> > @@ -1573,14 +1573,9 @@ static void do_remove_conflicting_framebuffers(struct apertures_struct *a,
> > }
> > }
> >
> > -static bool lockless_register_fb;
> > -module_param_named_unsafe(lockless_register_fb, lockless_register_fb, bool, 0400);
> > -MODULE_PARM_DESC(lockless_register_fb,
> > - "Lockless framebuffer registration for debugging [default=off]");
> > -
> > static int do_register_framebuffer(struct fb_info *fb_info)
> > {
> > - int i, ret;
> > + int i;
> > struct fb_videomode mode;
> >
> > if (fb_check_foreignness(fb_info))
> > @@ -1649,17 +1644,7 @@ static int do_register_framebuffer(struct fb_info *fb_info)
> > }
> > #endif
> >
> > - if (!lockless_register_fb)
> > - console_lock();
> > - else
> > - atomic_inc(&ignore_console_lock_warning);
> > - ret = fbcon_fb_registered(fb_info);
> > -
> > - if (!lockless_register_fb)
> > - console_unlock();
> > - else
> > - atomic_dec(&ignore_console_lock_warning);
> > - return ret;
> > + return fbcon_fb_registered(fb_info);
> > }
> >
> > static void unbind_console(struct fb_info *fb_info)
> > @@ -1669,9 +1654,7 @@ static void unbind_console(struct fb_info *fb_info)
> > if (WARN_ON(i < 0 || i >= FB_MAX || registered_fb[i] != fb_info))
> > return;
> >
> > - console_lock();
> > fbcon_fb_unbind(fb_info);
> > - console_unlock();
> > }
> >
> > static void unlink_framebuffer(struct fb_info *fb_info)
> > @@ -1714,9 +1697,7 @@ static void do_unregister_framebuffer(struct fb_info *fb_info)
> > fb_notifier_call_chain(FB_EVENT_FB_UNREGISTERED, &event);
> > }
> > #endif
> > - console_lock();
> > fbcon_fb_unregistered(fb_info);
> > - console_unlock();
> >
> > /* this may free fb info */
> > put_fb_info(fb_info);
> > --
> > 2.33.0

--
Daniel Vetter
Software Engineer, Intel Corporation