linux-kernel - Re: [PATCH v2] i2c: i2c-qcom-geni: Fix DMA transfer race

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Date:   Sun, 26 Jul 2020 14:47:48 +0200
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     swboyd@...omium.org, msavaliy@...eaurora.org,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        Akash Asthana <akashast@...eaurora.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Alok Chauhan <alokc@...eaurora.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Girish Mahadevan <girishm@...eaurora.org>,
        Karthikeyan Ramasubramanian <kramasub@...eaurora.org>,
        Sagar Dharia <sdharia@...eaurora.org>,
        linux-arm-msm@...r.kernel.org, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] i2c: i2c-qcom-geni: Fix DMA transfer race

On Thu, Jul 23, 2020 at 09:56:34PM +0200, Wolfram Sang wrote:
> On Wed, Jul 22, 2020 at 03:00:21PM -0700, Douglas Anderson wrote:
> > When I have KASAN enabled on my kernel and I start stressing the
> > touchscreen my system tends to hang.  The touchscreen is one of the
> > only things that does a lot of big i2c transfers and ends up hitting
> > the DMA paths in the geni i2c driver.  It appears that KASAN adds
> > enough delay in my system to tickle a race condition in the DMA setup
> > code.
> > 
> > When the system hangs, I found that it was running the geni_i2c_irq()
> > over and over again.  It had these:
> > 
> > m_stat   = 0x04000080
> > rx_st    = 0x30000011
> > dm_tx_st = 0x00000000
> > dm_rx_st = 0x00000000
> > dma      = 0x00000001
> > 
> > Notably we're in DMA mode but are getting M_RX_IRQ_EN and
> > M_RX_FIFO_WATERMARK_EN over and over again.
> > 
> > Putting some traces in geni_i2c_rx_one_msg() showed that when we
> > failed we were getting to the start of geni_i2c_rx_one_msg() but were
> > never executing geni_se_rx_dma_prep().
> > 
> > I believe that the problem here is that we are starting the geni
> > command before we run geni_se_rx_dma_prep().  If a transfer makes it
> > far enough before we do that then we get into the state I have
> > observed.  Let's change the order, which seems to work fine.
> > 
> > Although problems were seen on the RX path, code inspection suggests
> > that the TX should be changed too.  Change it as well.
> > 
> > Fixes: 37692de5d523 ("i2c: i2c-qcom-geni: Add bus driver for the Qualcomm GENI I2C controller")
> > Signed-off-by: Douglas Anderson <dianders@...omium.org>
> > Tested-by: Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
> > Reviewed-by: Akash Asthana <akashast@...eaurora.org>
> 
> Applied to for-current, thanks!

Glad we got this sorted. I just wondered that Alok wasn't part of the
discussion. Is he still interested in maintaining the driver? Also
because there is an unprocessed patch left for this driver:

http://patchwork.ozlabs.org/project/linux-i2c/patch/20191103212204.13606-1-colin.king@canonical.com/


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