[Intel-gfx] [PATCH 14/21] fbcon: use lock_fb_info in fbcon_open/release

Daniel Vetter
2022-01-31T21:07:10Z

Now we get to the real motiviation, because fbmem.c insists that
that's the right lock for these.

Ofc fbcon.c has a lot more places where it probably should call
lock_fb_info(). But looking at fbmem.c at least most of these seem to
be protected by console_lock() too, which is probably what papers over
any issues.

Note that this means we're shuffling around a bit the locking sections
for some of the console takeover and unbind paths, but not all:
- console binding/unbinding from the console layer never with
lock_fb_info
- unbind (as opposed to unlink) never bother with lock_fb_info

Also the real serialization against set_par and set_pan are still
doing by wrapping the entire ioctl code in console_lock(). So this
shuffling shouldn't be worse than what we had from a "can you trigger
races?" pov, but it's at least clearer.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Claudio Suarez <cssk@net-c.es>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Du Cheng <ducheng2@gmail.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: William Kucharski <william.kucharski@oracle.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Zheyu Ma <zheyuma97@gmail.com>
Cc: Zhen Lei <thunder.leizhen@huawei.com>
Cc: Xiyu Yang <xiyuyang19@fudan.edu.cn>
---
drivers/video/fbdev/core/fbcon.c | 5 +++++
drivers/video/fbdev/core/fbmem.c | 4 ----
2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index 5a3391ff038d..496bc5f2133e 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -682,8 +682,10 @@ static int fbcon_invalid_charcount(struct fb_info *info, unsigned charcount)

static void fbcon_release(struct fb_info *info)
{
+ lock_fb_info(info);
if (info->fbops->fb_release)
info->fbops->fb_release(info, 0);
+ unlock_fb_info(info);

module_put(info->fbops->owner);
}
@@ -695,11 +697,14 @@ static int fbcon_open(struct fb_info *info)
if (!try_module_get(info->fbops->owner))
return -ENODEV;

+ lock_fb_info(info);
if (info->fbops->fb_open &&
info->fbops->fb_open(info, 0)) {
+ unlock_fb_info(info);
module_put(info->fbops->owner);
return -ENODEV;
}
+ unlock_fb_info(info);

ops = kzalloc(sizeof(struct fbcon_ops), GFP_KERNEL);
if (!ops) {
diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
index 0fa7ede94fa6..fd51d12f2702 100644
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -1653,9 +1653,7 @@ static int do_register_framebuffer(struct fb_info *fb_info)
console_lock();
else
atomic_inc(&ignore_console_lock_warning);
- lock_fb_info(fb_info);
ret = fbcon_fb_registered(fb_info);
- unlock_fb_info(fb_info);

if (!lockless_register_fb)
console_unlock();
@@ -1672,9 +1670,7 @@ static void unbind_console(struct fb_info *fb_info)
return;

console_lock();
- lock_fb_info(fb_info);
fbcon_fb_unbind(fb_info);
- unlock_fb_info(fb_info);
console_unlock();
}

--
2.33.0