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

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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.

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