On Thu, May 19, 2016 at 10:22 PM, Scot Doyle <lkml14 at scotdoyle.com> wrote: > 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 at ucw.cz> >> >> > 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:
If 'jiffies' is passed to mod_timer() for same timer unusually OR mod_timer() isn't called from the timer handler, it shoudln't cause soft lockup. In the case of fbcon, 'jiffies' is always passed to mod_timer() and mod_timer() is called from the timer handler meantime, that is a real lockup. > > 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? >
