Hi,
I'm consistently and constantly hitting a deadlock.
console_callback in drivers/tty/vt/vt.c does: console_lock() and then calls:
do_blank_screen, which calls:
vc->vc_sw->con_blank(..) which can be a pointer to the function:
fbcon_blank in video/console/fbcon.c. This is missing a
WARN_CONSOLE_UNLOCKED. This calls:
fbcon_generic_blank which does lock_fb_info(info)
So we have a console_lock() followed by a lock_fb_info(info).
Now if while that is running, we have an ioctl call:
do_fb_ioctl in drivers/video/fbmem.c which does:
if (!lock_fb_info(info))
return -ENODEV;
console_lock();
So it tries to acquire the same locks in the reverse order. This
deadlocks consistently for me.
(I'm also curious why I'm hitting this continually, when everyone else
seems to be okay.)
I understand that this is really difficult to fix, but if anyone has
even a suggestion on how to hack it to make it work for me, I'd be
very grateful.
Thank you,
John Tapsell
On 09/11/2013 05:25 AM, John Tapsell wrote:
> Hi,
> I'm consistently and constantly hitting a deadlock.
>
> console_callback in drivers/tty/vt/vt.c does: console_lock() and then calls:
> do_blank_screen, which calls:
> vc->vc_sw->con_blank(..) which can be a pointer to the function:
> fbcon_blank in video/console/fbcon.c. This is missing a
> WARN_CONSOLE_UNLOCKED. This calls:
> fbcon_generic_blank which does lock_fb_info(info)
>
> So we have a console_lock() followed by a lock_fb_info(info).
>
> Now if while that is running, we have an ioctl call:
>
> do_fb_ioctl in drivers/video/fbmem.c which does:
> if (!lock_fb_info(info))
> return -ENODEV;
> console_lock();
>
>
> So it tries to acquire the same locks in the reverse order. This
> deadlocks consistently for me.
>
> (I'm also curious why I'm hitting this continually, when everyone else
> seems to be okay.)
>
> I understand that this is really difficult to fix, but if anyone has
> even a suggestion on how to hack it to make it work for me, I'd be
> very grateful.
As a temporary workaround, you can disable timed console blanking on the
kernel command line with 'consoleblank=0'.
Regards,
Peter Hurley
The following seems to be better:
>From d93c1e9761ff66365d658da7d8d0d33823aa946f Mon Sep 17 00:00:00 2001
From: John Tapsell <[email protected]>
Date: Thu, 12 Sep 2013 09:16:12 +0100
Subject: [PATCH] Fix deadlock between fb_info and console. Do not lock
fb_info when calling sending the FB_EVENT_CONBLANK
In fbmem.c, the semantics are that we acquire the lock_fb_info first,
and then console_lock. However when fbcon.c fbcon_generic_blank() is
called, the console lock could already be held. Locking fb_info can
thus cause a deadlock.
fbmem.c sends the FB_EVENT_BLANK without locking lock_fb_info first, so
this change introduces similar behaviour.
---
drivers/video/console/fbcon.c | 4 ----
1 file changed, 4 deletions(-)
diff --git a/drivers/video/console/fbcon.c b/drivers/video/console/fbcon.c
index 6b4fb5c..8546441 100644
--- a/drivers/video/console/fbcon.c
+++ b/drivers/video/console/fbcon.c
@@ -2333,13 +2333,9 @@ static void fbcon_generic_blank(struct vc_data *vc,
struct fb_info *info,
vc->vc_video_erase_char = oldc;
}
-
- if (!lock_fb_info(info))
- return;
event.info = info;
event.data = ␣
fb_notifier_call_chain(FB_EVENT_CONBLANK, &event);
- unlock_fb_info(info);
}
static int fbcon_blank(struct vc_data *vc, int blank, int mode_switch)
--
1.8.1.2
How can I get this reviewed/acked please?
--
View this message in context: http://linux-kernel.2935.n7.nabble.com/Deadlock-in-fb-and-tty-tp717929p718779.html
Sent from the Linux Kernel mailing list archive at Nabble.com.
On 09/12/2013 09:22 AM, johnflux wrote:
> The following seems to be better:
>
> From d93c1e9761ff66365d658da7d8d0d33823aa946f Mon Sep 17 00:00:00 2001
> From: John Tapsell<[email protected]>
> Date: Thu, 12 Sep 2013 09:16:12 +0100
> Subject: [PATCH] Fix deadlock between fb_info and console. Do not lock
> fb_info when calling sending the FB_EVENT_CONBLANK
>
> In fbmem.c, the semantics are that we acquire the lock_fb_info first,
> and then console_lock. However when fbcon.c fbcon_generic_blank() is
> called, the console lock could already be held. Locking fb_info can
> thus cause a deadlock.
>
> fbmem.c sends the FB_EVENT_BLANK without locking lock_fb_info first, so
> this change introduces similar behaviour.
> ---
> drivers/video/console/fbcon.c | 4 ----
> 1 file changed, 4 deletions(-)
>
> diff --git a/drivers/video/console/fbcon.c b/drivers/video/console/fbcon.c
> index 6b4fb5c..8546441 100644
> --- a/drivers/video/console/fbcon.c
> +++ b/drivers/video/console/fbcon.c
> @@ -2333,13 +2333,9 @@ static void fbcon_generic_blank(struct vc_data *vc,
> struct fb_info *info,
> vc->vc_video_erase_char = oldc;
> }
>
> -
> - if (!lock_fb_info(info))
> - return;
> event.info = info;
> event.data = ␣
> fb_notifier_call_chain(FB_EVENT_CONBLANK, &event);
> - unlock_fb_info(info);
> }
>
> static int fbcon_blank(struct vc_data *vc, int blank, int mode_switch)
> -- 1.8.1.2
> How can I get this reviewed/acked please?
The get_maintainer.pl script can help to discover to whom to
address patches. For example,
peter@thor:~/src/kernels/next$ ./scripts/get_maintainer.pl -f drivers/video/console/fbcon.c
Jean-Christophe Plagniol-Villard <[email protected]> (maintainer:FRAMEBUFFER LAYER)
Tomi Valkeinen <[email protected]> (maintainer:FRAMEBUFFER LAYER)
Dave Airlie <[email protected]> (commit_signer:5/11=45%)
Greg Kroah-Hartman <[email protected]> (commit_signer:4/11=36%)
Wang YanQing <[email protected]> (commit_signer:4/11=36%)
Andrew Morton <[email protected]> (commit_signer:3/11=27%)
Kamal Mostafa <[email protected]> (commit_signer:1/11=9%)
[email protected] (open list:FRAMEBUFFER LAYER)
[email protected] (open list)
In this case, you'll want to send this patch addressed to the two maintainers
and cc linux-fbdev and linux-kernel. You can cc me if you want.
This is covered in Documentation/SubmittingPatches, which also covers the
required subject line format <hint: too long, needs subsystem identifier>.
Also, if you have the lockdep report of the deadlock, it's customary to
include it in the commit message.
Regards,
Peter Hurley
PS - Don't put stuff after the '--' tag at the end of the patch. Many
mailers treat that as don't care. I missed your question first time around
because Thunderbird grays that text :(