Re: [PATCH v2 1/1] fbdev/core: Disable console-lock warnings when fb.lockless_register_fb is set

Hi,

On 19-07-18 10:53, Petr Mladek wrote:

On Wed 2018-07-18 11:30:02, Thomas Zimmermann wrote:

quoted

If the console is unlocked during registration, the console subsystem
generates significant amounts of warnings, which obfuscate actual
debugging messages. Setting ignore_console_lock_warning while debugging
console registration avoid the noise.

v2:
	- restore ignore_console_lock_warning if lock_fb_info() fails

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
---
  drivers/video/fbdev/core/fbmem.c | 15 +++++++++++----
  1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
index 9e2f9d3c760e..432c26eeabfb 100644
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c

@@ -1627,6 +1627,7 @@ static int do_register_framebuffer(struct fb_info *fb_info)
  	int i, ret;
  	struct fb_event event;
  	struct fb_videomode mode;
+	bool saved_ignore_console_lock_warning = ignore_console_lock_warning;

Hmm, this approach is racy if there are other users
saving/setting/restoring ignore_console_lock_warning in parallel.
I mean that this works only when the entire safe/set/restore
operation is nested or sequential.

We might need another approach if there are more users,
e.g. use an atomic counter for ignore_console_lock_warning.

I noticed this would be racy too, but this only gets used when
console-locking should be disabled when registering fbdev-s
for debugging purposes at which point everything console related
is racy already anyways, so I think this is fine as is.

On the other hand, I wonder if there ever will be other user.
Also it is "just" for debugging. We could keep it simple for now.
It might be enough to add a comment into include/linux/console.h,
something like:

Ack, lets keep this simple / as is in v2 of the patch.

Regards,

Hans

/*
  * Set ignore_console_lock_warning to true if you need to quiet
  * WARN_CONSOLE_UNLOCKED() for debugging purposes. Might need
  * another approach if manipulated by more users in parallel.
  */

Best Regards,
Petr