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).
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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