linux.git/drivers/video/fbdev/core/fbcon.c, branch v5.19

fbcon: Use fbcon_info_from_console() in fbcon_modechange_possible()

2022-07-07T08:52:35+00:00

Use the fbcon_info_from_console() wrapper which was added to kernel
v5.19 with commit 409d6c95f9c6 ("fbcon: Introduce wrapper for console->fb_info lookup").

Signed-off-by: Helge Deller 
Reviewed-by: Geert Uytterhoeven

fbcon: Prevent that screen size is smaller than font size

2022-07-07T08:50:46+00:00

We need to prevent that users configure a screen size which is smaller than the
currently selected font size. Otherwise rendering chars on the screen will
access memory outside the graphics memory region.

This patch adds a new function fbcon_modechange_possible() which
implements this check and which later may be extended with other checks
if necessary.  The new function is called from the FBIOPUT_VSCREENINFO
ioctl handler in fbmem.c, which will return -EINVAL if userspace asked
for a too small screen size.

Signed-off-by: Helge Deller 
Reviewed-by: Geert Uytterhoeven 
Cc: stable@vger.kernel.org # v5.4+

fbcon: Disallow setting font bigger than screen size

2022-07-07T08:50:45+00:00

Prevent that users set a font size which is bigger than the physical screen.
It's unlikely this may happen (because screens are usually much larger than the
fonts and each font char is limited to 32x32 pixels), but it may happen on
smaller screens/LCD displays.

Signed-off-by: Helge Deller 
Reviewed-by: Daniel Vetter 
Reviewed-by: Geert Uytterhoeven 
Cc: stable@vger.kernel.org # v4.14+

fbcon: replace snprintf in show functions with sysfs_emit

2022-04-14T19:56:19+00:00

Use sysfs_emit instead of scnprintf or sprintf.

Reported-by: Zeal Robot 
Signed-off-by: Yang Guang 
Signed-off-by: Helge Deller 
Link: https://patchwork.freedesktop.org/patch/msgid/0cb7ca73d9cd7162988a22a24cd18bbcd3d8bb27.1638156341.git.yang.guang5@zte.com.cn

fbcon: Fix delayed takeover locking

2022-04-13T20:54:48+00:00

I messed up the delayed takover path in the locking conversion in
6e7da3af008b ("fbcon: Move console_lock for register/unlink/unregister").

If CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER is enabled, fbcon take-over
doesn't take place when calling fbcon_fb_registered(). Instead, is deferred
using a workqueue and its fbcon_register_existing_fbs() function calls to
fbcon_fb_registered() again for each registered fbcon fb.

This leads to the console_lock tried to be held twice, causing a deadlock.

Fix it by re-extracting the lockless function and using it in the
delayed takeover path, where we need to hold the lock already to
iterate over the list of already registered fb. Well the current code
still is broken in there (since the list is protected by a
registration_lock, which we can't take here because it nests the other
way round with console_lock), but in the future this will be a list
protected by console_lock when this is all sorted out.

While reviewing the broken commit I realized that I've left some
outdated comments about the locking behind. Fix those too.

v2: Improve commit message (Javier)

Reported-by: Nathan Chancellor 
Tested-by: Nathan Chancellor 
Reviewed-by: Javier Martinez Canillas 
Cc: Nathan Chancellor 
Fixes: 6e7da3af008b ("fbcon: Move console_lock for register/unlink/unregister")
Cc: Sam Ravnborg 
Cc: Thomas Zimmermann 
Cc: Du Cheng 
Cc: Claudio Suarez 
Cc: Greg Kroah-Hartman 
Cc: Tetsuo Handa 
Cc: Matthew Wilcox 
Cc: Zheyu Ma 
Cc: Guenter Roeck 
Cc: Helge Deller 
Cc: Geert Uytterhoeven 
Cc: Javier Martinez Canillas 
Signed-off-by: Daniel Vetter 
Link: https://patchwork.freedesktop.org/patch/msgid/20220413082128.348186-1-daniel.vetter@ffwll.ch

fbcon: use min() to make code cleaner

2022-04-12T19:40:56+00:00

Use min() in order to make code cleaner.

Reported-by: Zeal Robot 
Signed-off-by: Changcheng Deng 
Reviewed-by: Sam Ravnborg 
Signed-off-by: Helge Deller 
Link: https://patchwork.freedesktop.org/patch/msgid/20220209084810.1561184-1-deng.changcheng@zte.com.cn

fbcon: Maintain a private array of fb_info

2022-04-07T14:52:14+00:00

Accessing the one in fbmem.c without taking the right locks is a bad
idea. Instead maintain our own private copy, which is fully protected
by console_lock() (like everything else in fbcon.c). That copy is
serialized through fbcon_fb_registered/unregistered() calls.

Also this means we do not need to hold a full fb_info reference, which
is nice because doing so would mean a refcount loop between the
console and the fb_info. But it's also not nice since it means
console_lock() must be held absolutely everywhere. Well strictly
speaking we could still try to do some refcounting games again by
calling get_fb_info before we drop the console_lock. But things will
get tricky.

Acked-by: Sam Ravnborg 
Signed-off-by: Daniel Vetter 
Cc: Daniel Vetter 
Cc: Tetsuo Handa 
Cc: Claudio Suarez 
Cc: Du Cheng 
Cc: Greg Kroah-Hartman 
Link: https://patchwork.freedesktop.org/patch/msgid/20220405210335.3434130-18-daniel.vetter@ffwll.ch

fbcon: untangle fbcon_exit

2022-04-07T14:52:13+00:00

There's a bunch of confusions going on here:
- The deferred fbcon setup notifier should only be cleaned up from
  fb_console_exit(), to be symmetric with fb_console_init()
- We also need to make sure we don't race with the work, which means
  temporarily dropping the console lock (or we can deadlock)
- That also means no point in clearing deferred_takeover, we are
  unloading everything anyway.
- Finally rename fbcon_exit to fbcon_release_all and move it, since
  that's what's it doing when being called from consw->con_deinit
  through fbcon_deinit.

To answer a question from Sam just quoting my own reply:

> We loose the call to fbcon_release_all() here [in fb_console_exit()].
> We have part of the old fbcon_exit() above, but miss the release parts.

Ah yes that's the entire point of this change. The release_all in the
fbcon exit path was only needed when fbcon was a separate module
indepedent from core fb.ko. Which means it was possible to unload fbcon
while having fbdev drivers registered.

But since we've merged them that has become impossible, so by the time the
fb.ko module can be unloaded, there's guaranteed to be no fbdev drivers
left. And hence removing them is pointless.

v2: Explain the why better (Sam)

Acked-by: Sam Ravnborg 
Signed-off-by: Daniel Vetter 
Cc: Daniel Vetter 
Cc: Greg Kroah-Hartman 
Cc: Claudio Suarez 
Cc: Du Cheng 
Cc: Tetsuo Handa 
Link: https://patchwork.freedesktop.org/patch/msgid/20220405210335.3434130-17-daniel.vetter@ffwll.ch

fbcon: Move more code into fbcon_release

2022-04-07T14:52:13+00:00

con2fb_release_oldinfo() has a bunch more kfree() calls than
fbcon_exit(), but since kfree() on NULL is harmless doing that in both
places should be ok. This is also a bit more symmetric now again with
fbcon_open also allocating the fbcon_ops structure.

Acked-by: Sam Ravnborg 
Signed-off-by: Daniel Vetter 
Cc: Daniel Vetter 
Cc: Tetsuo Handa 
Cc: Greg Kroah-Hartman 
Cc: Du Cheng 
Cc: Claudio Suarez 
Link: https://patchwork.freedesktop.org/patch/msgid/20220405210335.3434130-16-daniel.vetter@ffwll.ch

fbcon: Move console_lock for register/unlink/unregister

2022-04-07T14:52:13+00:00

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().

Acked-by: Sam Ravnborg 
Signed-off-by: Daniel Vetter 
Cc: Daniel Vetter 
Cc: Thomas Zimmermann 
Cc: Du Cheng 
Cc: Claudio Suarez 
Cc: Greg Kroah-Hartman 
Cc: Tetsuo Handa 
Cc: Matthew Wilcox 
Cc: Sam Ravnborg 
Cc: Zheyu Ma 
Cc: Guenter Roeck 
Cc: Alex Deucher 
Cc: Zhen Lei 
Cc: Xiyu Yang 
Link: https://patchwork.freedesktop.org/patch/msgid/20220405210335.3434130-15-daniel.vetter@ffwll.ch