Re: [PATCH v5 2/3] fbcon: Call WARN_CONSOLE_UNLOCKED() where applicable

On Wed, 11 Jul 2018 16:46:11 +0200
Thomas Zimmermann [off-list ref] wrote:

Hi

Am 28.06.2018 um 11:03 schrieb Hans de Goede:

quoted

Replace comments about places where the console lock should be held with
calls to WARN_CONSOLE_UNLOCKED() to assert that it is actually held.  

Debugging fbcon sometimes requires to not take the console lock. This
patch breaks the debugging workaround provided by
'fb.lockless_register_fb'. The dmesg is now filled with warnings about
the missing lock.

What if you make lockless_register_fb visible to fbcon, and then we can
have a macro:

#define WARN_FB_CONSOLE_UNLOCKED() 			\
	do {						\
		if (unlikely(!lockless_register_fb))	\
			WARN_CONSOLE_UNLOCKED();	\
	} while (0)

And use that instead?

-- Steve

Best regards
Thomas

quoted

Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Daniel Vetter <redacted>
Reviewed-by: Sergey Senozhatsky <redacted>
Signed-off-by: Hans de Goede <redacted>
---
Changes in v3:
-New patch in v3 of this patchset

Changes in v4:
-Keep the comments about which fbcon functions need locks in place
---
 drivers/video/fbdev/core/fbcon.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index c910e74d46ff..cd8d52a967aa 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c

@@ -828,6 +828,8 @@ static int set_con2fb_map(int unit, int newidx, int user)
 	struct fb_info *oldinfo = NULL;
  	int found, err = 0;
 
+	WARN_CONSOLE_UNLOCKED();
+
 	if (oldidx = newidx)
 		return 0;
 

@@ -3044,6 +3046,8 @@ static int fbcon_fb_unbind(int idx)
 {
 	int i, new_idx = -1, ret = 0;
 
+	WARN_CONSOLE_UNLOCKED();
+
 	if (!fbcon_has_console_bind)
 		return 0;
 

@@ -3094,6 +3098,8 @@ static int fbcon_fb_unregistered(struct fb_info *info)
 {
 	int i, idx;
 
+	WARN_CONSOLE_UNLOCKED();
+
 	idx = info->node;
 	for (i = first_fb_vc; i <= last_fb_vc; i++) {
 		if (con2fb_map[i] = idx)

@@ -3131,6 +3137,9 @@ static int fbcon_fb_unregistered(struct fb_info *info)
 static void fbcon_remap_all(int idx)
 {
 	int i;
+
+	WARN_CONSOLE_UNLOCKED();
+
 	for (i = first_fb_vc; i <= last_fb_vc; i++)
 		set_con2fb_map(i, idx, 0);
 

@@ -3177,6 +3186,8 @@ static int fbcon_fb_registered(struct fb_info *info)
 {
 	int ret = 0, i, idx;
 
+	WARN_CONSOLE_UNLOCKED();
+
 	idx = info->node;
 	fbcon_select_primary(info);