Hi,
On Tue, May 17, 2016 at 4:07 AM, Dann Frazier
<dann.frazier@xxxxxxxxxxxxx> wrote:
> Hi,
> I'm observing a soft lockup issue w/ the ASPEED controller on an
> arm64 server platform. This was originally seen on Ubuntu's 4.4
> kernel, but it is reproducible w/ vanilla 4.6-rc7 as well.
>
> [ 32.792656] NMI watchdog: BUG: soft lockup - CPU#38 stuck for 22s!
> [swapper/38:0]
>
> I observe this just once each time I boot into debian-installer (I'm
> using a serial console, but the ast module gets loaded during
> startup).
I have figured out that it is caused by 'mod_timer(timer, jiffies)' and
'ops->cur_blink_jiffies' is observed as zero in cursor_timer_handler()
when the issue happened.
Looks it is a real fbcon/vt issue, see following:
fbcon_init()
<-.con_init
<-visual_init()
reset_terminal()
<-vc_init()
vc->vc_cur_blink_ms is just set in reset_terminal() from vc_init() path,
and ops->cur_blink_jiffies is figured out from vc->vc_cur_blink_ms
in fbcon_init().
And visual_init() is always run before vc_init(), so ops->cur_blink_jiffies
is initialized as zero and cause the soft lockup issue finally.
Thanks,
Ming
>
> perf shows that the CPU caught by the NMI is typically in code
> updating the cursor timer:
>
> - 16.92% swapper [kernel.kallsyms] [k] _raw_spin_unlock_irqrestore
> - _raw_spin_unlock_irqrestore
> + 16.87% mod_timer
> + 0.05% cursor_timer_handler
> - 12.15% swapper [kernel.kallsyms] [k] queue_work_on
> - queue_work_on
> + 12.00% cursor_timer_handler
> + 0.15% call_timer_fn
> + 10.98% swapper [kernel.kallsyms] [k] run_timer_softirq
> - 2.23% swapper [kernel.kallsyms] [k] mod_timer
> - mod_timer
> + 1.97% cursor_timer_handler
> + 0.26% call_timer_fn
>
> During the same period, I can see that another CPU is actively
> executing the timer function:
>
> - 42.18% kworker/u96:2 [kernel.kallsyms] [k] ww_mutex_unlock
> - ww_mutex_unlock
> - 40.70% ast_dirty_update
> ast_imageblit
> soft_cursor
> bit_cursor
> fb_flashcursor
> process_one_work
> worker_thread
> kthread
> ret_from_fork
> + 1.48% ast_imageblit
> - 40.15% kworker/u96:2 [kernel.kallsyms] [k] __memcpy_toio
> - __memcpy_toio
> + 31.54% ast_dirty_update
> + 8.61% ast_imageblit
>
> Using the graph function tracer on fb_flashcursor(), I see that
> ast_dirty_update usually takes around 60 us, in which it makes 16
> calls to __memcpy_toio(). However, there is always one instance on
> every boot of the installer where ast_dirty_update() takes ~98 *ms* to
> complete, during which it makes 743 calls to __memcpy_toio(). While
> that doesn't directly account for the full 22s, I do wonder if that
> maybe a smoking gun.
>
> fyi, this is being tracked at: https://bugs.launchpad.net/bugs/1574814
>
> -dann
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