[PATCH] fbcon: Fix delayed takeover locking

* [PATCH] fbcon: Fix delayed takeover locking
@ 2022-04-13  8:21 ` Daniel Vetter
  0 siblings, 0 replies; 15+ messages in thread
From: Daniel Vetter @ 2022-04-13  8:21 UTC (permalink / raw)
  To: DRI Development
  Cc: Du Cheng, Tetsuo Handa, Daniel Vetter,
	Intel Graphics Development, Zheyu Ma, Javier Martinez Canillas,
	Matthew Wilcox, Nathan Chancellor, Claudio Suarez, Daniel Vetter,
	Thomas Zimmermann, Greg Kroah-Hartman, Geert Uytterhoeven,
	Sam Ravnborg, Helge Deller, Guenter Roeck

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

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.

Reported-by: Nathan Chancellor <nathan@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Fixes: 6e7da3af008b ("fbcon: Move console_lock for register/unlink/unregister")
Cc: Sam Ravnborg <sam@ravnborg.org>
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: Zheyu Ma <zheyuma97@gmail.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Helge Deller <deller@gmx.de>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Javier Martinez Canillas <javierm@redhat.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
---
 drivers/video/fbdev/core/fbcon.c | 28 ++++++++++++++++++----------
 1 file changed, 18 insertions(+), 10 deletions(-)

diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index 6a7d470beec7..b4e43b39d9a8 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -2772,7 +2772,6 @@ static void fbcon_unbind(void)
 static inline void fbcon_unbind(void) {}
 #endif /* CONFIG_VT_HW_CONSOLE_BINDING */
 
-/* called with console_lock held */
 void fbcon_fb_unbind(struct fb_info *info)
 {
 	int i, new_idx = -1;
@@ -2822,7 +2821,6 @@ void fbcon_fb_unbind(struct fb_info *info)
 	console_unlock();
 }
 
-/* called with console_lock held */
 void fbcon_fb_unregistered(struct fb_info *info)
 {
 	int i, idx;
@@ -2928,14 +2926,11 @@ 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)
+static int do_fb_registered(struct fb_info *info)
 {
 	int ret = 0, i, idx;
 
-	if (!lockless_register_fb)
-		console_lock();
-	else
-		atomic_inc(&ignore_console_lock_warning);
+	WARN_CONSOLE_UNLOCKED();
 
 	fbcon_registered_fb[info->node] = info;
 	fbcon_num_registered_fb++;
@@ -2945,7 +2940,7 @@ int fbcon_fb_registered(struct fb_info *info)
 
 	if (deferred_takeover) {
 		pr_info("fbcon: Deferring console take-over\n");
-		goto out;
+		return 0;
 	}
 
 	if (info_idx == -1) {
@@ -2965,7 +2960,20 @@ int fbcon_fb_registered(struct fb_info *info)
 		}
 	}
 
-out:
+	return ret;
+}
+
+int fbcon_fb_registered(struct fb_info *info)
+{
+	int ret;
+
+	if (!lockless_register_fb)
+		console_lock();
+	else
+		atomic_inc(&ignore_console_lock_warning);
+
+	ret = do_fb_registered(info);
+
 	if (!lockless_register_fb)
 		console_unlock();
 	else
@@ -3280,7 +3288,7 @@ static void fbcon_register_existing_fbs(struct work_struct *work)
 	logo_shown = FBCON_LOGO_DONTSHOW;
 
 	fbcon_for_each_registered_fb(i)
-		fbcon_fb_registered(fbcon_registered_fb[i]);
+		do_fb_registered(fbcon_registered_fb[i]);
 
 	console_unlock();
 }
-- 
2.34.1


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