[PATCH Xenial SRU] tty: vt: Fix soft lockup in fbcon cursor blink timer.

[Ming Lei]

On Tue, May 24, 2016 at 7:11 PM, Chris J Arges
<chris.j.arges at canonical.com> wrote:
> On Tue, May 24, 2016 at 12:55:54PM +0800, Ming Lei wrote:
>> From: David Daney <david.daney at cavium.com>
>>
>> BugLink: http://bugs.launchpad.net/bugs/1574814
>>
>> We are getting somewhat random soft lockups with this signature:
>>
>> [   86.992215] [<fffffc00080935e0>] el1_irq+0xa0/0x10c
>> [   86.997082] [<fffffc000841822c>] cursor_timer_handler+0x30/0x54
>> [   87.002991] [<fffffc000810ec44>] call_timer_fn+0x54/0x1a8
>> [   87.008378] [<fffffc000810ef88>] run_timer_softirq+0x1c4/0x2bc
>> [   87.014200] [<fffffc000809077c>] __do_softirq+0x114/0x344
>> [   87.019590] [<fffffc00080af45c>] irq_exit+0x74/0x98
>> [   87.024458] [<fffffc00080fac20>] __handle_domain_irq+0x98/0xfc
>> [   87.030278] [<fffffc000809056c>] gic_handle_irq+0x94/0x190
>>
>> This is caused by the vt visual_init() function calling into
>> fbcon_init() with a vc_cur_blink_ms value of zero.  This is a
>> transient condition, as it is later set to a non-zero value.  But, if
>> the timer happens to expire while the blink rate is zero, it goes into
>> an endless loop, and we get soft lockup.
>>
>> The fix is to initialize vc_cur_blink_ms before calling the con_init()
>> function.
>>
>> Tested-by: Ming Lei <ming.lei at canonical.com>
>> Acked-by: Pavel Machek <pavel at ucw.cz>
>> Acked-by: Scot Doyle <lkml14 at scotdoyle.com>
>> Signed-off-by: David Daney <david.daney at cavium.com>
>> Cc: stable at vger.kernel.org
>
> When you cherry-pick onto Xenial can you also include the -x flag to append the
> commit hash?

This patch doesn't land linus tree yet, and it does block di installer &
mass enablement, so hope it can land xenial first.

Thanks,

> --chris
>
>> ---
>>  drivers/tty/vt/vt.c | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
>> index 4af9a8f..d80f4ec 100644
>> --- a/drivers/tty/vt/vt.c
>> +++ b/drivers/tty/vt/vt.c
>> @@ -761,6 +761,7 @@ static void visual_init(struct vc_data *vc, int num, int init)
>>       vc->vc_complement_mask = 0;
>>       vc->vc_can_do_color = 0;
>>       vc->vc_panic_force_write = false;
>> +     vc->vc_cur_blink_ms = DEFAULT_CURSOR_BLINK_MS;
>>       vc->vc_sw->con_init(vc, init);
>>       if (!vc->vc_complement_mask)
>>               vc->vc_complement_mask = vc->vc_can_do_color ? 0x7700 : 0x0800;
>> --
>> 1.9.1
>>
>>
>> --
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