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Date: Tue, 27 Aug 2019 15:52:17 +0100
From: Russell King - ARM Linux admin <linux@...linux.org.uk>
To: Ulf Hansson <ulf.hansson@...aro.org>
Cc: "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: Continuous SD IO causes hung task messages
On Tue, Aug 27, 2019 at 03:36:34PM +0100, Russell King - ARM Linux admin wrote:
> On Tue, Aug 27, 2019 at 03:55:23PM +0200, Ulf Hansson wrote:
> > On Tue, 27 Aug 2019 at 15:43, Russell King - ARM Linux admin
> > <linux@...linux.org.uk> wrote:
> > >
> > > Hi,
> > >
> > > While dd'ing the contents of a SD card, I get hung task timeout
> > > messages as per below. However, the dd is making progress. Any
> > > ideas?
> > >
> > > Presumably, mmc_rescan doesn't get a look-in while IO is progressing
> > > for the card?
> >
> > Is it a regression?
> >
> > There not much of recent mmc core and mmc block changes, that I can
> > think of at this point.
>
> No idea - I just repaired the SD socket after the D2 line became
> disconnected, and decided to run that command as a test.
>
> > > ARM64 host, Macchiatobin, uSD card.
> >
> > What mmc host driver is it? mmci?
>
> sdhci-xenon.
>
> I'm just trying with one CPU online, then I'll try with two. My
> suspicion is that there's a problem in the ARM64 arch code where
> unlocking a mutex doesn't get noticed on other CPUs.
>
> Hmm, I thought I'd try bringing another CPU online, but it seems
> like the ARM64 CPU hotplug code is broken:
>
> [ 3552.029689] CPU1: shutdown
> [ 3552.031099] psci: CPU1 killed.
> [ 3949.835212] CPU1: failed to come online
> [ 3949.837753] CPU1: failed in unknown state : 0x0
>
> which means I can only take CPUs down, I can't bring them back
> online without rebooting.
Okay, running on a single CPU shows no problems.
Running on four CPUs (as originally) shows that the kworker thread
_never_ gets scheduled, so the warning is not false.
With three CPUs, same problem.
root@...-d06300000000:~# ps aux | grep ' D '
root 34 0.0 0.0 0 0 ? D 15:38 0:00 [kworker/1:1+events_freezable]
root@...-d06300000000:~# cat /proc/34/sched
kworker/1:1 (34, #threads: 1)
-------------------------------------------------------------------
se.exec_start : 318689.992440
se.vruntime : 37750.882357
se.sum_exec_runtime : 9.421240
se.nr_migrations : 0
nr_switches : 1174
nr_voluntary_switches : 1171
nr_involuntary_switches : 3
se.load.weight : 1048576
se.runnable_weight : 1048576
se.avg.load_sum : 6
se.avg.runnable_load_sum : 6
se.avg.util_sum : 5170
se.avg.load_avg : 0
se.avg.runnable_load_avg : 0
se.avg.util_avg : 0
se.avg.last_update_time : 318689991680
se.avg.util_est.ewma : 10
se.avg.util_est.enqueued : 0
policy : 0
prio : 120
clock-delta : 0
The only thing that changes there is "clock-delta". When I kill the
dd, I get:
root@...-d06300000000:~# cat /proc/34/sched
kworker/1:1 (34, #threads: 1)
-------------------------------------------------------------------
se.exec_start : 574025.791680
se.vruntime : 79996.657300
se.sum_exec_runtime : 10.916400
se.nr_migrations : 0
nr_switches : 1403
nr_voluntary_switches : 1400
nr_involuntary_switches : 3
se.load.weight : 1048576
se.runnable_weight : 1048576
se.avg.load_sum : 15
se.avg.runnable_load_sum : 15
se.avg.util_sum : 15007
se.avg.load_avg : 0
se.avg.runnable_load_avg : 0
se.avg.util_avg : 0
se.avg.last_update_time : 574025791488
se.avg.util_est.ewma : 10
se.avg.util_est.enqueued : 0
policy : 0
prio : 120
clock-delta : 40
so the thread makes forward progress.
Down to two CPUs:
root@...-d06300000000:~# ps aux | grep ' D '
root 34 0.0 0.0 0 0 ? D 15:38 0:00 [kworker/1:1+events_freezable]
Same symptoms. dd and md5sum switch between CPU 0 and CPU1.
--
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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