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

[David Daney]

On 05/18/2016 01:24 PM, Scot Doyle wrote:
> On Wed, 18 May 2016, Ming Lei wrote:
> > On Wed, May 18, 2016 at 4:49 AM, Pavel Machek <pavel@xxxxxx> wrote:
> > > On Tue 2016-05-17 11:41:04, David Daney wrote:
> > > > From: David Daney <david.daney@xxxxxxxxxx>
> > > >
> > > > 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.
> > > >
> > > > Signed-off-by: David Daney <david.daney@xxxxxxxxxx>
> > > > Cc: stable@xxxxxxxxxxxxxxx
> > >
> > > Acked-by: Pavel Machek <pavel@xxxxxx>
> >
> > Tested-by: Ming Lei <ming.lei@xxxxxxxxxxxxx>
> >
> > Thanks David and Pavel for making it work!
> >
> > > (And it is amazing how many problems configurable blink speed caused).
> > >
> > > Thanks!
> > >                                                                 Pavel
>
>
> Dann, Ming and David, thank you so much for all of your effort.
>
> There were three other reports in the past year, each leading to their own
> patch,

Why were none of the patches merged?  Were they obviously incorrect, or 
is there some other problem that blocks the resolution of this issue?

> of boot lockups occuring when the cursor flash timer was set using
> an ops->cur_blink_jiffies value of 0.  I plan to propose a patch within
> the next day that will prevent this for all code paths.