linux-kernel - Re: Regression v5.12-rc3: net: stmmac: re-init rx buffers when mac resume back

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Date:   Thu, 1 Apr 2021 17:28:33 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Joakim Zhang <qiangqing.zhang@....com>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Jose Abreu <joabreu@...opsys.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-tegra <linux-tegra@...r.kernel.org>,
        Jakub Kicinski <kuba@...nel.org>
Subject: Re: Regression v5.12-rc3: net: stmmac: re-init rx buffers when mac
 resume back


On 31/03/2021 12:41, Joakim Zhang wrote:

...

>> In answer to your question, resuming from suspend does work on this board
>> without your change. We have been testing suspend/resume now on this board
>> since Linux v5.8 and so we have the ability to bisect such regressions. So it is
>> clear to me that this is the change that caused this, but I am not sure why.
> 
> Yes, I know this issue is regression caused by my patch. I just want to analyze the potential reasons. Due to the code change only related to the page recycle and reallocate.
> So I guess if this page operate need IOMMU works when IOMMU is enabled. Could you help check if IOMMU driver resume before STMMAC? Our common desire is to find the root cause, right?


Yes of course that is the desire here indeed. I had assumed that the
suspend/resume order was good because we have never seen any problems,
but nonetheless it is always good to check. Using ftrace I enabled
tracing of the appropriate suspend/resume functions and this is what
I see ...

# tracer: function
#
# entries-in-buffer/entries-written: 4/4   #P:6
#
#                                _-----=> irqs-off
#                               / _----=> need-resched
#                              | / _---=> hardirq/softirq
#                              || / _--=> preempt-depth
#                              ||| /     delay
#           TASK-PID     CPU#  ||||   TIMESTAMP  FUNCTION
#              | |         |   ||||      |         |
         rtcwake-748     [000] ...1   536.700777: stmmac_pltfr_suspend <-platform_pm_suspend
         rtcwake-748     [000] ...1   536.735532: arm_smmu_pm_suspend <-platform_pm_suspend
         rtcwake-748     [000] ...1   536.757290: arm_smmu_pm_resume <-platform_pm_resume
         rtcwake-748     [003] ...1   536.856771: stmmac_pltfr_resume <-platform_pm_resume


So I don't see any ordering issues that could be causing this. 

Jon

-- 
nvpublic