Re: [PATCH] fbcon: use default if cursor blink interval is not valid

[Scot Doyle]

On Thu, 19 May 2016, Pavel Machek wrote:
> Hi!
> 
> > Two current [1] and three previous [2] systems locked during boot
> > because the cursor flash timer was set using an ops->cur_blink_jiffies
> > value of 0. Previous patches attempted to solve the problem by moving
> > variable initialization earlier in the setup sequence [2].
> > 
> > Use the normal cursor blink default interval of 200 ms if
> > ops->cur_blink_jiffies is not in the range specified in commit
> > bd63364caa8d. Since invalid values are not used, specific system
> > initialization timings should not cause lockups.
> > 
> > [1] https://bugs.launchpad.net/bugs/1574814
> > [2] see commits: 2a17d7e80f1d, f235f664a8af, a1e533ec07d5
> 
> Acked-by: Pavel Machek <pavel@xxxxxx>
> 
> >  static void cursor_timer_handler(unsigned long dev_addr)
> >  {
> >  	struct fb_info *info = (struct fb_info *) dev_addr;
> >  	struct fbcon_ops *ops = info->fbcon_par;
> >  
> >  	queue_work(system_power_efficient_wq, &info->queue);
> > -	mod_timer(&ops->cursor_timer, jiffies + ops->cur_blink_jiffies);
> > +	mod_timer(&ops->cursor_timer, jiffies +
> > +	    cursor_blink_jiffies(ops->cur_blink_jiffies));
> >  }
> >  
> >  static void fbcon_add_cursor_timer(struct fb_info *info)
> 
> And actually... perhaps mod_timer should have some check for too low
> timeouts..?
> 
> WARN_ON?
> 									Pavel


Interesting idea. I applied this patch to a couple systems and 
receive the same warning on both:

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 73164c3..f6c0b69 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -788,6 +788,7 @@ __mod_timer(struct timer_list *timer, unsigned long expires,
 
 	timer_stats_timer_set_start_info(timer);
 	BUG_ON(!timer->function);
+	WARN_ONCE(expires == jiffies, "timer should expire in the future");
 
 	base = lock_timer_base(timer, &flags);
 
------

[    2.060474] ------------[ cut here ]------------
[    2.061613] WARNING: CPU: 0 PID: 164 at kernel/time/timer.c:791 mod_timer+0x233/0x240
[    2.062740] timer should expire in the future
[    2.062757] CPU: 0 PID: 164 Comm: kworker/0:2 Not tainted 4.6.0+ #7
[    2.065870] Hardware name: Toshiba Leon, BIOS          12/04/2013
[    2.067828] Workqueue: events_power_efficient hub_init_func3
[    2.069762]  0000000000000000 ffff88007443bbb8 ffffffff8139932b ffff88007443bc08
[    2.071701]  0000000000000000 ffff88007443bbf8 ffffffff8112e57c 0000031700000000
[    2.073655]  ffff88007486a0b0 00000000fffea2da ffff88007486a000 0000000000000202
[    2.075594] Call Trace:
[    2.077503]  [<ffffffff8139932b>] dump_stack+0x4d/0x72
[    2.079426]  [<ffffffff8112e57c>] __warn+0xcc/0xf0
[    2.081325]  [<ffffffff8112e5ef>] warn_slowpath_fmt+0x4f/0x60
[    2.083212]  [<ffffffff813ad5e5>] ? find_next_bit+0x15/0x20
[    2.085022]  [<ffffffff8139914f>] ? cpumask_next_and+0x2f/0x40
[    2.086696]  [<ffffffff81188a93>] mod_timer+0x233/0x240
[    2.088362]  [<ffffffff815fff02>] usb_hcd_submit_urb+0x3f2/0x8c0
[    2.090026]  [<ffffffff81601dc4>] ? urb_destroy+0x24/0x30
[    2.091698]  [<ffffffff81142ba8>] ? insert_work+0x58/0xb0
[    2.093349]  [<ffffffff81602297>] usb_submit_urb+0x287/0x530
[    2.094985]  [<ffffffff815f986d>] hub_activate+0x1fd/0x5d0
[    2.096625]  [<ffffffff81150188>] ? finish_task_switch+0x78/0x1f0
[    2.098268]  [<ffffffff815f9cca>] hub_init_func3+0x1a/0x20
[    2.099908]  [<ffffffff811438e0>] process_one_work+0x140/0x3e0
[    2.101539]  [<ffffffff81143bce>] worker_thread+0x4e/0x480
[    2.103173]  [<ffffffff81143b80>] ? process_one_work+0x3e0/0x3e0
[    2.104790]  [<ffffffff81143b80>] ? process_one_work+0x3e0/0x3e0
[    2.106259]  [<ffffffff81149829>] kthread+0xc9/0xe0
[    2.107731]  [<ffffffff81856152>] ret_from_fork+0x22/0x40
[    2.109215]  [<ffffffff81149760>] ? __kthread_parkme+0x70/0x70
[    2.110704] ---[ end trace 3519886a1a990d99 ]---

mod_timer is called from over a thousand places. Should timers always 
expire in the future?