Re: [PATCH] fbcon: Avoid deleting a timer in IRQ context

[Tomeu Vizoso]

On 27 May 2015 at 13:19, Andrey Wagin <avagin@xxxxxxxxx> wrote:
> 2015-05-21 10:58 GMT+03:00 Thierry Reding <thierry.reding@xxxxxxxxx>:
>> From: Thierry Reding <treding@xxxxxxxxxx>
>>
>> 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.
>
> Tested-by: Andrew Vagin <avagin@xxxxxxxxxxxxx>
>
> It would be good to push this patch into linux-next asap. Without this
> patch I can't execute tests on linux-next. Thanks.

Tested-by: Tomeu Vizoso <tomeu.vizoso@xxxxxxxxxxxxx>

Same here, please apply.

Thanks,

Tomeu

>>
>> Reported-by: Daniel Stone <daniel@xxxxxxxxxxxxx>
>> Reported-by: Kevin Hilman <khilman@xxxxxxxxxx>
>> Tested-by: Kevin Hilman <khilman@xxxxxxxxxx>
>> Tested-by: Scot Doyle <lkml14@xxxxxxxxxxxxx>
>> Signed-off-by: Thierry Reding <treding@xxxxxxxxxx>
>> ---
>>  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
>>
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