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Message-ID: <573B5DF0.3080808@caviumnetworks.com> Date: Tue, 17 May 2016 11:07:44 -0700 From: David Daney <ddaney@...iumnetworks.com> To: Peter Hurley <peter@...leysoftware.com>, Dann Frazier <dann.frazier@...onical.com> CC: Ming Lei <ming.lei@...onical.com>, Scot Doyle <lkml14@...tdoyle.com>, David Airlie <airlied@...ux.ie>, <dri-devel@...ts.freedesktop.org>, "Chintakuntla, Radha" <Radha.Chintakuntla@...iumnetworks.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Jiri Slaby <jslaby@...e.com>, Pavel Machek <pavel@....cz>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: ast: cursor flashing softlockups On 05/17/2016 10:39 AM, David Daney wrote: > I can confirm this. I have a patch that I think is the proper fix. You should see it soon (after I test it a bit more) Thanks, David Daney [...] >>> >>> On Tue, May 17, 2016 at 4:07 AM, Dann Frazier >>> <dann.frazier@...onical.com> 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. >> >> Thanks for tracking this down. >> >> This softlockup looks to be caused by: >> >> commit 27a4c827c34ac4256a190cc9d24607f953c1c459 >> Author: Scot Doyle <lkml14@...tdoyle.com> >> Date: Thu Mar 26 13:56:38 2015 +0000 >> >> fbcon: use the cursor blink interval provided by vt >> >> vt now provides a cursor blink interval via vc_data. Use this >> interval instead of the currently hardcoded 200 msecs. Store >> it in >> fbcon_ops to avoid locking the console in cursor_timer_handler(). >> >> Signed-off-by: Scot Doyle <lkml14@...tdoyle.com> >> Acked-by: Pavel Machek <pavel@....cz> >> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org> >> >> and >> >> commit bd63364caa8df38bad2b25b11b2a1b849475cce5 >> Author: Scot Doyle <lkml14@...tdoyle.com> >> Date: Thu Mar 26 13:54:39 2015 +0000 >> >> vt: add cursor blink interval escape sequence >> >> Add an escape sequence to specify the current console's cursor >> blink >> interval. The interval is specified as a number of >> milliseconds until >> the next cursor display state toggle, from 50 to 65535. >> /proc/loadavg >> did not show a difference with a one msec interval, but the lower >> bound is set to 50 msecs since slower hardware wasn't tested. >> >> Store the interval in the vc_data structure for later access >> by fbcon, >> initializing the value to fbcon's current hardcoded value of >> 200 msecs. >> >> Signed-off-by: Scot Doyle <lkml14@...tdoyle.com> >> Acked-by: Pavel Machek <pavel@....cz> >> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org> >> >> >> >>> 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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