linux-kernel - Re: next/master boot: 254 boots: 16 failed, 231 passed with 4 offline, 1 untried/unknown, 2 conflicts (next-20190726)

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Date:   Sun, 18 Aug 2019 21:35:08 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Mark Brown <broonie@...nel.org>
Cc:     Andy Gross <agross@...nel.org>,
        kernel-build-reports@...ts.linaro.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: next/master boot: 254 boots: 16 failed, 231 passed with 4
 offline, 1 untried/unknown, 2 conflicts (next-20190726)

On Fri 26 Jul 06:48 PDT 2019, Mark Brown wrote:

> On Fri, Jul 26, 2019 at 05:18:01AM -0700, kernelci.org bot wrote:
> 
> The past few versions of -next failed to boot on apq8096-db820c:
> 
> >     defconfig:
> >         gcc-8:
> >             apq8096-db820c: 1 failed lab
> 
> with an RCU stall towards the end of boot:
> 
> 00:03:40.521336  [   18.487538] qcom_q6v5_pas adsp-pil: adsp-pil supply px not found, using dummy regulator
> 00:04:01.523104  [   39.499613] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
> 00:04:01.533371  [   39.499657] rcu: 	2-...!: (0 ticks this GP) idle=9ca/1/0x4000000000000000 softirq=1450/1450 fqs=50
> 00:04:01.537544  [   39.504689] 	(detected by 0, t=5252 jiffies, g=2425, q=619)
> 00:04:01.541727  [   39.513539] Task dump for CPU 2:
> 00:04:01.547929  [   39.519096] seq             R  running task        0   199    198 0x00000000
> 
> Full details and logs at:
> 
> 	https://kernelci.org/boot/id/5d3aa7ea59b5142ba868890f/
> 
> The last version that worked was from the 15th and there seem to be
> similar issues in mainline since -rc1.

As you might have seen this problem has come and gone on the
apq8096-db820c and I've finally managed to narrow it down a little bit.

The problem first appears on next-20190701, with the introduction of
CONFIG_RANDOMIZE_BASE in the defconfig, but after further efforts I've
concluded that disabling kpti removes or hides the problem.

With kpti=no on the command line I've now successfully booted the db820c
100+ times without problems (a clear improvement from the 75% failure
rate with kpti=yes).

Unfortunately I'm not yet certain why this is causing issues and I'm
also seeing the same rcu stall on SDA845 under certain (erroneous?)
conditions (where I don't expect them). 

Regards,
Bjorn