linux-kernel - Re: [PATCH 4.9 00/25] 4.9.316-rc1 review

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Date:   Wed, 25 May 2022 10:05:15 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Ard Biesheuvel <ardb@...nel.org>, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, torvalds@...ux-foundation.org,
        akpm@...ux-foundation.org, linux@...ck-us.net, shuah@...nel.org,
        patches@...nelci.org, lkft-triage@...ts.linaro.org, pavel@...x.de,
        f.fainelli@...il.com, sudipm.mukherjee@...il.com,
        slade@...dewatkins.com,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH 4.9 00/25] 4.9.316-rc1 review


On 24/05/2022 16:06, Greg Kroah-Hartman wrote:
> On Tue, May 24, 2022 at 03:55:58PM +0100, Jon Hunter wrote:
>>
>> On 24/05/2022 13:09, Greg Kroah-Hartman wrote:
>>
>> ...
>>
>>>> I am seeing a boot regression on tegra124-jetson-tk1 and reverting the above
>>>> commit is fixing the problem. This also appears to impact linux-4.14.y,
>>>> 4.19.y and 5.4.y.
>>>>
>>>> Test results for stable-v4.9:
>>>>       8 builds:	8 pass, 0 fail
>>>>       18 boots:	16 pass, 2 fail
>>>>       18 tests:	18 pass, 0 fail
>>>>
>>>> Linux version:	4.9.316-rc1-gbe4ec3e3faa1
>>>> Boards tested:	tegra124-jetson-tk1, tegra20-ventana,
>>>>                   tegra210-p2371-2180, tegra30-cardhu-a04
>>>>
>>>> Boot failures:	tegra124-jetson-tk1
>>>
>>> Odd.  This is also in 5.10.y, right?  No issues there?  Are we missing
>>> something?
>>
>>
>> Actually, the more I look at this, the more I see various intermittent
>> reports with this and it is also impacting the mainline.
>>
>> The problem is that the commit in question is causing a ton of messages to
>> be printed a boot and this sometimes is causing the boot test to fail
>> because the boot is taking too long. The console shows ...
>>
>> [ 1233.327547] CPU0: Spectre BHB: using loop workaround
>> [ 1233.327795] CPU1: Spectre BHB: using loop workaround
>> [ 1233.328270] CPU1: Spectre BHB: using loop workaround
>> [ 1233.328700] CPU1: Spectre BHB: using loop workaround
>> [ 1233.355477] CPU2: Spectre BHB: using loop workaround
>> ** 7 printk messages dropped **
>> [ 1233.366271] CPU0: Spectre BHB: using loop workaround
>> [ 1233.366580] CPU0: Spectre BHB: using loop workaround
>> [ 1233.366815] CPU1: Spectre BHB: using loop workaround
>> [ 1233.405475] CPU1: Spectre BHB: using loop workaround
>> [ 1233.405874] CPU0: Spectre BHB: using loop workaround
>> [ 1233.406041] CPU1: Spectre BHB: using loop workaround
>> ** 1 printk messages dropped **
>>
>> There is a similar report of this [0] and I believe that we need a similar
>> fix for the above prints as well. I have reported this to Ard [1]. So I am
>> not sure that these Spectre BHB patches are quite ready for stable.
> 
> These patches are quite small, and just enable it for this known-broken
> cpu type.
> 
> If there is an issue enabling it for this cpu type, then we can work on
> that upstream, but there shouldn't be a reason to prevent this from
> being merged now, especially given that it is supposed to be fixing a
> known issue.

Yes understand. I have been doing some more testing and with v4.9, this 
is triggering a boot timeout 100% of the time. So with 20 boots, all 20 
timeout. Note the timeout is 2 mins. With v4.14, I saw only 5 out of 20 
timeouts and so it would seem that v4.9 is slower to boot in general. I 
think that the more recent kernels show intermittent timeouts.

We have some verbose logging enabled on this platform, which until now 
has not been a problem, but I will disable this and that should resolve 
this for now.

Cheers
Jon	

-- 
nvpublic