Re: [PATCH v2 2/3] fbcon: use the cursor blink interval provided by vt

Thierry Reding
2015-05-20T12:36:17Z

[-- Attachment #1.1: Type: text/plain, Size: 3182 bytes --]

On Tue, May 19, 2015 at 04:41:12PM -0700, Greg Kroah-Hartman wrote:
> On Tue, May 19, 2015 at 11:52:29PM +0200, Thierry Reding wrote:
> > On Tue, May 19, 2015 at 02:45:19PM -0700, Kevin Hilman wrote:
> > > On Tue, May 19, 2015 at 2:40 PM, Thierry Reding
> > > <thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> > > > On Tue, May 19, 2015 at 02:15:41PM -0700, Kevin Hilman wrote:
> > > >> On Thu, Mar 26, 2015 at 6:56 AM, Scot Doyle <lkml14-enLWO88E2pdl57MIdRCFDg@public.gmane.org> wrote:
> > > >> > vt now provides a cursor blink interval via vc_data. Use this
> > > >> > interval instead of the currently hardcoded 200 msecs. Store it in
> > > >> > fbcon_ops to avoid locking the console in cursor_timer_handler().
> > > >> >
> > > >> > Signed-off-by: Scot Doyle <lkml14-enLWO88E2pdl57MIdRCFDg@public.gmane.org>
> > > >> > Acked-by: Pavel Machek <pavel-+ZI9xUNit7I@public.gmane.org>
> > > >>
> > > >> This patch hit next-20150519 in the form of commit 27a4c827c34a
> > > >> (fbcon: use the cursor blink interval provided by vt) and has caused
> > > >> boot failure on a handful of ARM platforms when booting a MMC root
> > > >> filesystem. This error was spotted by the kernelci.org bot on
> > > >> exynos5800-peach-pi[1] and Thierry and Daniel (Cc'd) have seen it on
> > > >> some tegra platforms too.
> > > >>
> > > >> Thierry spotted this commit as a potential cause, and both Daniel and
> > > >> I have reverted and boot tested on exynos5 and tegra respectively and
> > > >> the boot panics disappear.
> > > >
> > > > FWIW, if I apply the below on top of next-20150519 things seem to be
> > > > back to normal as well:
> > > >
> > > > diff --git a/drivers/video/console/fbcon.c b/drivers/video/console/fbcon.c
> > > > index 05b1d1a71ef9..658c34bb9076 100644
> > > > --- a/drivers/video/console/fbcon.c
> > > > +++ b/drivers/video/console/fbcon.c
> > > > @@ -1310,8 +1310,9 @@ static void fbcon_cursor(struct vc_data *vc, int mode)
> > > > return;
> > > >
> > > > ops->cur_blink_jiffies = msecs_to_jiffies(vc->vc_cur_blink_ms);
> > > > - fbcon_del_cursor_timer(info);
> > > > - if (!(vc->vc_cursor_type & 0x10))
> > > > + if (vc->vc_cursor_type & 0x10)
> > > > + fbcon_del_cursor_timer(info);
> > > > + else
> > > > fbcon_add_cursor_timer(info);
> > > >
> > > > ops->cursor_flash = (mode == CM_ERASE) ? 0 : 1;
> > >
> > > Applying this on next-20150519 makes my exynos board happily boot again as well.
> > >
> > > Tested-by: Kevin Hilman <khilman-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
> >
> > Excellent. Greg, Scot, any opinions on whether or not this is the right
> > thing to do? It restores a bit that looks suspiciously like it snuck in
> > in the original (at least it isn't documented in the commit message).
> >
> > Greg, feel free to squash this in if everybody agrees this is good to
> > go. If you prefer a patch on top let me know and I'll come up with a
> > proper commit message.
>
> Please send a real patch and I'll apply it on top, as I can't rebase my
> public tree.

Attached.

Thierry

[-- Attachment #1.2: 0001-fbcon-Avoid-deleting-a-timer-in-IRQ-context.patch --]
[-- Type: text/x-diff, Size: 3447 bytes --]

From 4f2f70dbbe9de54c0da9b03a1f384e1464755eab Mon Sep 17 00:00:00 2001
From: Thierry Reding <treding-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
Date: Wed, 20 May 2015 13:41:52 +0200
Subject: [PATCH] fbcon: Avoid deleting a timer in IRQ context

Commit 27a4c827c34a ("fbcon: use the cursor blink interval provided by
vt") unconditionally removes the cursor blink timer. Unfortunately that
wreaks havoc under some circumstances. An easily reproducible way is to
use both the framebuffer console and a debug serial port as the console
output for kernel messages (e.g. "console=ttyS0 console=tty1" on the
kernel command-line. Upon boot this triggers a warning from within the
del_timer_sync() function because it is called from IRQ context:

[ 5.070096] ------------[ cut here ]------------
[ 5.070110] WARNING: CPU: 0 PID: 0 at ../kernel/time/timer.c:1098 del_timer_sync+0x4c/0x54()
[ 5.070115] Modules linked in:
[ 5.070120] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.1.0-rc4-next-20150519 #1
[ 5.070123] Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
[ 5.070142] [] (unwind_backtrace) from [] (show_stack+0x10/0x14)
[ 5.070156] [] (show_stack) from [] (dump_stack+0x70/0xbc)
[ 5.070164] [] (dump_stack) from [] (warn_slowpath_common+0x74/0xb0)
[ 5.070169] [] (warn_slowpath_common) from [] (warn_slowpath_null+0x1c/0x24)
[ 5.070174] [] (warn_slowpath_null) from [] (del_timer_sync+0x4c/0x54)
[ 5.070183] [] (del_timer_sync) from [] (fbcon_del_cursor_timer+0x2c/0x40)
[ 5.070190] [] (fbcon_del_cursor_timer) from [] (fbcon_cursor+0x9c/0x180)
[ 5.070198] [] (fbcon_cursor) from [] (hide_cursor+0x30/0x98)
[ 5.070204] [] (hide_cursor) from [] (vt_console_print+0x2a8/0x340)
[ 5.070212] [] (vt_console_print) from [] (call_console_drivers.constprop.23+0xc8/0xec)
[ 5.070218] [] (call_console_drivers.constprop.23) from [] (console_unlock+0x498/0x4f0)
[ 5.070223] [] (console_unlock) from [] (vprintk_emit+0x1f0/0x508)
[ 5.070228] [] (vprintk_emit) from [] (vprintk_default+0x24/0x2c)
[ 5.070234] [] (vprintk_default) from [] (printk+0x70/0x88)

After which the system starts spewing all kinds of weird and seemingly
unrelated error messages.

This commit fixes this by restoring the condition under which the call
to fbcon_del_cursor_timer() happens.

Reported-by: Daniel Stone <daniel-rLtY4a/8tF1rovVCs/uTlw@public.gmane.org>
Reported-by: Kevin Hilman <khilman-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Tested-by: Kevin Hilman <khilman-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
Tested-by: Scot Doyle <lkml14-enLWO88E2pdl57MIdRCFDg@public.gmane.org>
Signed-off-by: Thierry Reding <treding-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
---
drivers/video/console/fbcon.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/video/console/fbcon.c b/drivers/video/console/fbcon.c
index 05b1d1a71ef9..658c34bb9076 100644
--- a/drivers/video/console/fbcon.c
+++ b/drivers/video/console/fbcon.c
@@ -1310,8 +1310,9 @@ static void fbcon_cursor(struct vc_data *vc, int mode)
return;

ops->cur_blink_jiffies = msecs_to_jiffies(vc->vc_cur_blink_ms);
- fbcon_del_cursor_timer(info);
- if (!(vc->vc_cursor_type & 0x10))
+ if (vc->vc_cursor_type & 0x10)
+ fbcon_del_cursor_timer(info);
+ else
fbcon_add_cursor_timer(info);

ops->cursor_flash = (mode == CM_ERASE) ? 0 : 1;
--
2.4.1

[-- Attachment #2: Type: application/pgp-signature, Size: 819 bytes --]