On Wed, Jul 11, 2018 at 5:01 PM, Hans de Goede [off-list ref] wrote:

Hi,

On 11-07-18 16:52, Steven Rostedt wrote:

quoted

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

quoted

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?

Yes I'm already preparing a patch like that :)

Without the unlikely though, this is not used in hot paths.

Note that you don't even need an EXPORT_SYMBOL since this is all in
the same module.
-Daniel

Regards,

Hans

quoted

-- Steve

quoted

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);

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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch