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[209.85.221.180]) by smtp.gmail.com with ESMTPSA id a133sm573790vsd.5.2020.12.10.09.14.27 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 10 Dec 2020 09:14:28 -0800 (PST) Received: by mail-vk1-f180.google.com with SMTP id i62so1385736vkb.7 for ; Thu, 10 Dec 2020 09:14:27 -0800 (PST) X-Received: by 2002:ac5:ce9b:: with SMTP id 27mr10106859vke.9.1607620467257; Thu, 10 Dec 2020 09:14:27 -0800 (PST) MIME-Version: 1.0 References: <20201203074459.13078-1-rojay@codeaurora.org> <160757022002.1580929.8656750350166301192@swboyd.mtv.corp.google.com> In-Reply-To: <160757022002.1580929.8656750350166301192@swboyd.mtv.corp.google.com> From: Doug Anderson Date: Thu, 10 Dec 2020 09:14:15 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH] spi: spi-geni-qcom: Fix NULL pointer access in geni_spi_isr To: Stephen Boyd Cc: Roja Rani Yarubandi , Mark Brown , Andy Gross , Bjorn Andersson , linux-arm-msm , linux-spi , LKML , Akash Asthana , msavaliy@qti.qualcomm.com Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-arm-msm@vger.kernel.org Hi, On Wed, Dec 9, 2020 at 7:17 PM Stephen Boyd wrote: > > Quoting Doug Anderson (2020-12-03 08:40:46) > > > I would guess that if "mas->cur_xfer" is NULL then > > geni_spi_handle_rx() should read all data in the FIFO and throw it > > away and geni_spi_handle_tx() should set SE_GENI_TX_WATERMARK_REG to > > 0. NOTE: I _think_ that with the synchronize_irq() I'm suggesting > > above we'll avoid this case, but it never hurts to be defensive. > > > > > > Does that all make sense? So the summary is that instead of your patch: > > Can we get a CPU diagram describing the race and scenario where this > happens? Something like: > > CPU0 CPU1 > ---- ---- > setup_fifo_xfer() > spin_lock_irq(&mas->lock); > spin_unlock_irq(&mas->lock); > mas->cur_xfer = xfer > ... > > geni_spi_isr() > geni_spi_handle_rx() > > > But obviously this example diagram is incorrect and some timeout happens > instead? Sorry, I'm super lazy and don't want to read many paragraphs of > text. :) I'd rather have a diagram like above that clearly points out > the steps taken to the NULL pointer deref. This is my untested belief of what's happening CPU0 CPU1 ---- ---- setup_fifo_xfer() ... geni_se_setup_m_cmd() spin_unlock_irq()