linux-kernel - [PATCH v2 12/19] fbcon: use lock_fb_info in fbcon

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Message-Id: <20220208210824.2238981-13-daniel.vetter@ffwll.ch>
Date:   Tue,  8 Feb 2022 22:08:17 +0100
From:   Daniel Vetter <daniel.vetter@...ll.ch>
To:     DRI Development <dri-devel@...ts.freedesktop.org>
Cc:     Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
        linux-fbdev@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Sam Ravnborg <sam@...nborg.org>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Claudio Suarez <cssk@...-c.es>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Du Cheng <ducheng2@...il.com>,
        Matthew Wilcox <willy@...radead.org>,
        William Kucharski <william.kucharski@...cle.com>,
        Alex Deucher <alexander.deucher@....com>,
        Zheyu Ma <zheyuma97@...il.com>,
        Zhen Lei <thunder.leizhen@...wei.com>,
        Xiyu Yang <xiyuyang19@...an.edu.cn>
Subject: [PATCH v2 12/19] fbcon: use lock_fb_info in fbcon_open/release

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.

Acked-by: Sam Ravnborg <sam@...nborg.org>
Signed-off-by: Daniel Vetter <daniel.vetter@...el.com>
Cc: Daniel Vetter <daniel@...ll.ch>
Cc: Claudio Suarez <cssk@...-c.es>
Cc: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc: Thomas Zimmermann <tzimmermann@...e.de>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Du Cheng <ducheng2@...il.com>
Cc: Sam Ravnborg <sam@...nborg.org>
Cc: Matthew Wilcox <willy@...radead.org>
Cc: William Kucharski <william.kucharski@...cle.com>
Cc: Alex Deucher <alexander.deucher@....com>
Cc: Zheyu Ma <zheyuma97@...il.com>
Cc: Zhen Lei <thunder.leizhen@...wei.com>
Cc: Xiyu Yang <xiyuyang19@...an.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 f0213a0e3870..cc960bf49991 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -684,8 +684,10 @@ 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);
 }
@@ -697,11 +699,14 @@ 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 ad9aac06427a..37656883e7bd 100644
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -1674,9 +1674,7 @@ 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();
@@ -1693,9 +1691,7 @@ 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();
 }
 
-- 
2.34.1